Persistence

From enterprise
Jump to: navigation, search

Tactic Description

Persistence is any access, action, or configuration change to a system that gives an adversary a persistent presence on that system. Adversaries will often need to maintain access to systems through interruptions such as system restarts, loss of credentials, or other failures that would require a remote access tool to restart or alternate backdoor for them to regain access.

Techniques

Below is a list of all the Persistence techniques in enterprise:

NameTacticsTechnical Description
.bash_profile and .bashrcPersistence~/.bash_profile and ~/.bashrc are executed in a user's context when a new shell opens or when a user logs in so that their environment is set correctly. ~/.bash_profile is executed for login shells and ~/.bashrc is executed for interactive non-login shells. This means that when a user logs in (via username and password) to the console (either locally or remotely via something like SSH), ~/.bash_profile is executed before the initial command prompt is returned to the user. After that, every time a new shell is opened, ~/.bashrc is executed. This allows users more fine grained control over when they want certain commands executed.

Mac's Terminal.app is a little different in that it runs a login shell by default each time a new terminal window is opened, thus calling ~/.bash_profile each time instead of ~/.bashrc.

These files are meant to be written to by the local user to configure their own environment; however, adversaries can also insert code into these files to gain persistence each time a user logs in or opens a new shell.
Accessibility FeaturesPersistence
Privilege Escalation
Windows contains accessibility features that may be launched with a key combination before a user has logged in (for example, when the user is on the Windows logon screen). An adversary can modify the way these programs are launched to get a command prompt or backdoor without logging in to the system.

Two common accessibility programs are C:\Windows\System32\sethc.exe, launched when the shift key is pressed five times and C:\Windows\System32\utilman.exe, launched when the Windows + U key combination is pressed. The sethc.exe program is often referred to as "sticky keys", and has been used by adversaries for unauthenticated access through a remote desktop login screen.FireEye Hikit Rootkit

Depending on the version of Windows, an adversary may take advantage of these features in different ways because of code integrity enhancements. In newer versions of Windows, the replaced binary needs to be digitally signed for x64 systems, the binary must reside in %systemdir%\, and it must be protected by Windows File or Resource Protection (WFP/WRP).DEFCON2016 Sticky Keys The debugger method was likely discovered as a potential workaround because it does not require the corresponding accessibility feature binary to be replaced. Examples for both methods:

For simple binary replacement on Windows XP and later as well as and Windows Server 2003/R2 and later, for example, the program (e.g., C:\Windows\System32\utilman.exe) may be replaced with "cmd.exe" (or another program that provides backdoor access). Subsequently, pressing the appropriate key combination at the login screen while sitting at the keyboard or when connected over Remote Desktop Protocol will cause the replaced file to be executed with SYSTEM privileges.Tilbury 2014

For the debugger method on Windows Vista and later as well as Windows Server 2008 and later, for example, a Registry key may be modified that configures "cmd.exe," or another program that provides backdoor access, as a "debugger" for the accessibility program (e.g., "utilman.exe"). After the Registry is modified, pressing the appropriate key combination at the login screen while at the keyboard or when connected with RDP will cause the "debugger" program to be executed with SYSTEM privileges.Tilbury 2014

Other accessibility features exist that may also be leveraged in a similar fashion:DEFCON2016 Sticky Keys

  • On-Screen Keyboard: C:\Windows\System32\osk.exe
  • Magnifier: C:\Windows\System32\Magnify.exe
  • Narrator: C:\Windows\System32\Narrator.exe
  • Display Switcher: C:\Windows\System32\DisplaySwitch.exe
  • App Switcher: C:\Windows\System32\AtBroker.exe
AppInit DLLsPersistence
Privilege Escalation
DLLs that are specified in the AppInit_DLLs value in the Registry key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll. In practice this is nearly every program. This value can be abused to obtain persistence by causing a DLL to be loaded into most processes on the computer.AppInit Registry The AppInit DLL functionality is disabled in Windows 8 and later versions when secure boot is enabled.AppInit Secure Boot
Application ShimmingExecution
Persistence
Privilege Escalation
The Microsoft Windows Application Compatibility Infrastructure/Framework (Application Shim) was created to allow compatibility of programs as Windows updates and changes its code. For example, application shimming feature that allows programs that were created for Windows XP to work with Windows 10. Within the framework, shims are created to act as a buffer between the program (or more specifically, the Import Address Table) and the Windows OS. When a program is executed, the shim cache is referenced to determine if the program requires the use of the shim database (.sdb). If so, the shim database uses API hooking to redirect the code as necessary in order to communicate with the OS. A list of all shims currently installed by the default Windows installer (sdbinst.exe) is kept in:
  • %WINDIR%\AppPatch\sysmain.sdb
  • hklm\software\microsoft\windows nt\currentversion\appcompatflags\installedsdb

Custom databases are stored in:

  • %WINDIR%\AppPatch\custom & %WINDIR%\AppPatch\AppPatch64\Custom
  • hklm\software\microsoft\windows nt\currentversion\appcompatflags\custom
To keep shims secure, Windows designed them to run in user mode so they cannot modify the kernel and you must have administrator privileges to install a shim. However, certain shims can be used to Bypass User Account Control (UAC) (RedirectEXE), inject DLLs into processes (InjectDll), and intercept memory addresses (GetProcAddress). Utilizing these shims, an adversary can perform several malicious acts, such as elevate privileges, install backdoors, disable defenses like Windows Defender, etc.
Authentication PackagePersistenceWindows Authentication Package DLLs are loaded by the Local Security Authority (LSA) process at system start. They provide support for multiple logon processes and multiple security protocols to the operating system.MSDN Authentication Packages Adversaries can use the autostart mechanism provided by LSA Authentication Packages for persistence by placing a reference to a binary in the Windows Registry location HKLM\SYSTEM\CurrentControlSet\Control\Lsa\ with the key value of "Authentication Packages"=<target binary>. The binary will then be executed by the system when the authentication packages are loaded.
BootkitPersistenceA bootkit is a malware variant that modifies the boot sectors of a hard drive, including the Master Boot Record (MBR) and Volume Boot Record (VBR).MTrends 2016

Adversaries may use bootkits to persist on systems at a layer below the operating system, which may make it difficult to perform full remediation unless an organization suspects one was used and can act accordingly.

Master Boot Record

The MBR is the section of disk that is first loaded after completing hardware initialization by the BIOS. It is the location of the boot loader. An adversary who has raw access to the boot drive may overwrite this area, diverting execution during startup from the normal boot loader to adversary code.Lau 2011

Volume Boot Record

The MBR passes control of the boot process to the VBR. Similar to the case of MBR, an adversary who has raw access to the boot drive may overwrite the VBR to divert execution during startup to adversary code.
Change Default File AssociationPersistenceWhen a file is opened, the default program used to open the file (also called the file association or handler) is checked. File association selections are stored in the Windows Registry and can be edited by users, administrators, or programs that have Registry access.Microsoft Change Default ProgramsMicrosoft File Handlers Applications can modify the file association for a given file extension to call an arbitrary program when a file with the given extension is opened.
Component FirmwareDefense Evasion
Persistence
Some adversaries may employ sophisticated means to compromise computer components and install malicious firmware that will execute adversary code outside of the operating system and main system firmware or BIOS. This technique may be similar to System Firmware but conducted upon other system components that may not have the same capability or level of integrity checking. Malicious device firmware could provide both a persistent level of access to systems despite potential typical failures to maintain access and hard disk re-images, as well as a way to evade host software-based defenses and integrity checks.
Component Object Model HijackingDefense Evasion
Persistence
The Microsoft Component Object Model (COM) is a system within Windows to enable interaction between software components through the operating system.Microsoft Component Object Model Adversaries can use this system to insert malicious code that can be executed in place of legitimate software through hijacking the COM references and relationships as a means for persistence. Hijacking a COM object requires a change in the Windows Registry to replace a reference to a legitimate system component which may cause that component to not work when executed. When that system component is executed through normal system operation the adversary's code will be executed instead.GDATA COM Hijacking An adversary is likely to hijack objects that are used frequently enough to maintain a consistent level of persistence, but are unlikely to break noticeable functionality within the system as to avoid system instability that could lead to detection.
Cron JobPersistencePer Apple’s developer documentation, there are two supported methods for creating periodic background jobs: launchd and cronAppleDocs Scheduling Timed Jobs.

Launchd

Each Launchd job is described by a different configuration property list (plist) file similar to Launch Daemons or Launch Agents, except there is an additional key called StartCalendarInterval with a dictionary of time values AppleDocs Scheduling Timed Jobs. This only works on macOS and OS X.

cron

System-wide cron jobs are installed by modifying /etc/crontab while per-user cron jobs are installed using crontab with specifically formatted crontab files AppleDocs Scheduling Timed Jobs. This works on Mac and Linux systems.

Both methods allow for commands or scripts to be executed at specific, periodic intervals in the background without user interaction. An adversary may use task scheduling to execute programs at system startup or on a scheduled basis for persistenceJanicabMethods of Mac Malware PersistenceMalware Persistence on OS X, to conduct Execution as part of Lateral Movement, to gain root privileges, or to run a process under the context of a specific account.
DLL Search Order HijackingDefense Evasion
Persistence
Privilege Escalation
Windows systems use a common method to look for required DLLs to load into a program.Microsoft DLL Search Adversaries may take advantage of the Windows DLL search order and programs that ambiguously specify DLLs to gain privilege escalation and persistence.

Adversaries may perform DLL preloading, also called binary planting attacks,OWASP Binary Planting by placing a malicious DLL with the same name as an ambiguously specified DLL in a location that Windows searches before the legitimate DLL. Often this location is the current working directory of the program. Remote DLL preloading attacks occur when a program sets its current directory to a remote location such as a Web share before loading a DLL.Microsoft 2269637 Adversaries may use this behavior to cause the program to load a malicious DLL.

Adversaries may also directly modify the way a program loads DLLs by replacing an existing DLL or modifying a .manifest or .local redirection file, directory, or junction to cause the program to load a different DLL to maintain persistence or privilege escalation.Microsoft DLL RedirectionMicrosoft ManifestsMandiant Search Order

If a search order-vulnerable program is configured to run at a higher privilege level, then the adversary-controlled DLL that is loaded will also be executed at the higher level. In this case, the technique could be used for privilege escalation from user to administrator or SYSTEM or from administrator to SYSTEM, depending on the program.

Programs that fall victim to path hijacking may appear to behave normally because malicious DLLs may be configured to also load the legitimate DLLs they were meant to replace.
Dylib HijackingPersistence
Privilege Escalation
macOS and OS X use a common method to look for required dynamic libraries (dylib) to load into a program based on search paths. Adversaries can take advantage of ambiguous paths to plant dylibs to gain privilege escalation or persistence.

A common method is to see what dylibs an application uses, then plant a malicious version with the same name higher up in the search path. This typically results in the dylib being in the same folder as the application itselfWriting Bad Malware for OSXMalware Persistence on OS X.

If the program is configured to run at a higher privilege level than the current user, then when the dylib is loaded into the application, the dylib will also run at that elevated level. This can be used by adversaries as a privilege escalation technique.
External Remote ServicesPersistenceRemote services such as VPNs, Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. There are often remote service gateways that manage connections and credential authentication for these services. Adversaries may use remote services to access and persist within a network.Volexity Virtual Private Keylogging Access to Valid Accounts to use the service is often a requirement, which could be obtained through credential pharming or by obtaining the credentials from users after compromising the enterprise network. Access to remote services may be used as part of Redundant Access during an operation.
File System Permissions WeaknessPersistence
Privilege Escalation
Processes may automatically execute specific binaries as part of their functionality or to perform other actions. If the permissions on the file system directory containing a target binary, or permissions on the binary itself, are improperly set, then the target binary may be overwritten with another binary using user-level permissions and executed by the original process. If the original process and thread are running under a higher permissions level, then the replaced binary will also execute under higher-level permissions, which could include SYSTEM.

Adversaries may use this technique to replace legitimate binaries with malicious ones as a means of executing code at a higher permissions level. If the executing process is set to run at a specific time or during a certain event (e.g., system bootup) then this technique can also be used for persistence.

Services

Manipulation of Windows service binaries is one variation of this technique. Adversaries may replace a legitimate service executable with their own executable to gain persistence and/or privilege escalation to the account context the service is set to execute under (local/domain account, SYSTEM, LocalService, or NetworkService). Once the service is started, either directly by the user (if appropriate access is available) or through some other means, such as a system restart if the service starts on bootup, the replaced executable will run instead of the original service executable.

Executable Installers

Another variation of this technique can be performed by taking advantage of a weakness that is common in executable, self-extracting installers. During the installation process, it is common for installers to use a subdirectory within the %TEMP% directory to unpack binaries such as DLLs, EXEs, or other payloads. When installers create subdirectories and files they often do not set appropriate permissions to restrict write access, which allows for execution of untrusted code placed in the subdirectories or overwriting of binaries used in the installation process. This behavior is related to and may take advantage of DLL Search Order Hijacking. Some installers may also require elevated privileges that will result in privilege escalation when executing adversary controlled code. This behavior is related to Bypass User Account Control. Several examples of this weakness in existing common installers have been reported to software vendors.Mozilla Firefox Installer DLL HijackSeclists Kanthak 7zip Installer
Hidden Files and DirectoriesDefense Evasion
Persistence
To prevent normal users from accidentally changing special files on a system, most operating systems have the concept of a ‘hidden’ file. These files don’t show up when a user browses the file system with a GUI or when using normal commands on the command line. Users must explicitly ask to show the hidden files either via a series of Graphical User Interface (GUI) prompts or with command line switches (dir /a for Windows and ls –a for Linux and macOS).

Windows

Users can mark specific files as hidden by using the attrib.exe binary. Simply do attrib +h filename to mark a file or folder as hidden. Similarly, the “+s” marks a file as a system file and the “+r” flag marks the file as read only. Like most windows binaries, the attrib.exe binary provides the ability to apply these changes recursively “/S”.

Linux/Mac

Users can mark specific files as hidden simply by putting a “.” as the first character in the file or folder name Sofacy Komplex TrojanAntiquated Mac Malware. Files and folder that start with a period, ‘.’, are by default hidden from being viewed in the Finder application and standard command-line utilities like “ls”. Users must specifically change settings to have these files viewable. For command line usages, there is typically a flag to see all files (including hidden ones). To view these files in the Finder Application, the following command must be executed: defaults write com.apple.finder AppleShowAllFiles YES, and then relaunch the Finder Application.

Mac

Files on macOS can be marked with the UF_HIDDEN flag which prevents them from being seen in Finder.app, but still allows them to be seen in Terminal.appWireLurker. Many applications create these hidden files and folders to store information so that it doesn’t clutter up the user’s workspace. For example, SSH utilities create a .ssh folder that’s hidden and contains the user’s known hosts and keys.

Adversaries can use this to their advantage to hide files and folders anywhere on the system for persistence and evading a typical user or system analysis that does not incorporate investigation of hidden files.
HypervisorPersistenceA type-1 hypervisor is a software layer that sits between the guest operating systems and system's hardware.Wikipedia Hypervisor It presents a virtual running environment to an operating system. An example of a common hypervisor is Xen.Wikipedia Xen A type-1 hypervisor operates at a level below the operating system and could be designed with Rootkit functionality to hide its existence from the guest operating system.Myers 2007 A malicious hypervisor of this nature could be used to persist on systems through interruption.
LC_LOAD_DYLIB AdditionPersistenceMach-O binaries have a series of headers that are used to perform certain operations when a binary is loaded. The LC_LOAD_DYLIB header in a Mach-O binary tells macOS and OS X which dynamic libraries (dylibs) to load during execution time. These can be added ad-hoc to the compiled binary as long adjustments are made to the rest of the fields and dependenciesWriting Bad Malware for OSX. There are tools available to perform these changes. Any changes will invalidate digital signatures on binaries because the binary is being modified. Adversaries can remediate this issue by simply removing the LC_CODE_SIGNATURE command from the binary so that the signature isn’t checked at load timeMalware Persistence on OS X.
Launch AgentPersistencePer Apple’s developer documentation, when a user logs in, a per-user launchd process is started which loads the parameters for each launch-on-demand user agent from the property list (plist) files found in /System/Library/LaunchAgents, /Library/LaunchAgents, and $HOME/Library/LaunchAgentsAppleDocs Launch Agent DaemonsOSX Keydnap malwareAntiquated Mac Malware. These launch agents have property list files which point to the executables that will be launchedOSX.Dok Malware. Adversaries may install a new launch agent that can be configured to execute at login by using launchd or launchctl to load a plist into the appropriate directories Sofacy Komplex Trojan Methods of Mac Malware Persistence. The agent name may be disguised by using a name from a related operating system or benign software. Launch Agents are created with user level privileges and are executed with the privileges of the user when they log inOSX Malware DetectionOceanLotus for OS X. They can be set up to execute when a specific user logs in (in the specific user’s directory structure) or when any user logs in (which requires administrator privileges).
Launch DaemonPersistence
Privilege Escalation
Per Apple’s developer documentation, when macOS and OS X boot up, launchd is run to finish system initialization. This process loads the parameters for each launch-on-demand system-level daemon from the property list (plist) files found in /System/Library/LaunchDaemons and /Library/LaunchDaemonsAppleDocs Launch Agent Daemons. These LaunchDaemons have property list files which point to the executables that will be launchedMethods of Mac Malware Persistence.

Adversaries may install a new launch daemon that can be configured to execute at startup by using launchd or launchctl to load a plist into the appropriate directoriesOSX Malware Detection. The daemon name may be disguised by using a name from a related operating system or benign software WireLurker. Launch Daemons may be created with administrator privileges, but are executed under root privileges, so an adversary may also use a service to escalate privileges from administrator to root.

The plist file permissions must be root:wheel, but the script or program that it points to has no such requirement. So, it is possible for poor configurations to allow an adversary to modify a current Launch Daemon’s executable and gain persistence or Privilege Escalation.
LaunchctlDefense Evasion
Execution
Persistence
Launchctl controls the macOS launchd process which handles things like launch agents and launch daemons, but can execute other commands or programs itself. Launchctl supports taking subcommands on the command-line, interactively, or even redirected from standard input. By loading or reloading launch agents or launch daemons, adversaries can install persistence or execute changes they made Sofacy Komplex Trojan. Running a command from launchctl is as simple as launchctl submit -l <labelName> -- /Path/to/thing/to/execute "arg" "arg" "arg". Loading, unloading, or reloading launch agents or launch daemons can require elevated privileges. Adversaries can abuse this functionality to execute code or even bypass whitelisting if launchctl is an allowed process.
Local Port MonitorPersistence
Privilege Escalation
A port monitor can be set through the AddMonitor API call to set a DLL to be loaded at startup.AddMonitor This DLL can be located in C:\Windows\System32 and will be loaded by the print spooler service, spoolsv.exe, on boot.Bloxham Alternatively, an arbitrary DLL can be loaded if permissions allow writing a fully-qualified pathname for that DLL to HKLM\SYSTEM\CurrentControlSet\Control\Print\Monitors.Bloxham The spoolsv.exe process also runs under SYSTEM level permissions. Adversaries can use this technique to load malicious code at startup that will persist on system reboot and execute as SYSTEM.
Login ItemPersistenceMacOS provides the option to list specific applications to run when a user logs in. These applications run under the logged in user's context, and will be started every time the user logs in. Login items installed using the Service Management Framework are not visible in the System Preferences and can only be removed by the application that created themAdding Login Items. Users have direct control over login items installed using a shared file list which are also visible in System PreferencesAdding Login Items. These login items are stored in the user's ~/Library/Preferences/ directory in a plist file called com.apple.loginitems.plistMethods of Mac Malware Persistence. Some of these applications can open visible dialogs to the user, but they don’t all have to since there is an option to ‘Hide’ the window. If an adversary can register their own login item or modified an existing one, then they can use it to execute their code for a persistence mechanism each time the user logs inMalware Persistence on OS XOSX.Dok Malware.
Logon ScriptsLateral Movement
Persistence
===Windows===

Windows allows logon scripts to be run whenever a specific user or group of users log into a system.TechNet Logon Scripts The scripts can be used to perform administrative functions, which may often execute other programs or send information to an internal logging server.

If adversaries can access these scripts, they may insert additional code into the logon script to execute their tools when a user logs in. This code can allow them to maintain persistence on a single system, if it is a local script, or to move laterally within a network, if the script is stored on a central server and pushed to many systems. Depending on the access configuration of the logon scripts, either local credentials or an administrator account may be necessary.

Mac

Mac allows login and logoff hooks to be run as root whenever a specific user logs into or out of a system. A login hook tells Mac OS X to execute a certain script when a user logs in, but unlike startup items, a login hook executes as rootcreating login hook. There can only be one login hook at a time though. If adversaries can access these scripts, they can insert additional code to the script to execute their tools when a user logs in.
Modify Existing ServicePersistenceWindows service configuration information, including the file path to the service's executable, is stored in the Registry. Service configurations can be modified using utilities such as sc.exe and Reg. Adversaries can modify an existing service to persist malware on a system by using system utilities or by using custom tools to interact with the Windows API. Use of existing services is a type of Masquerading that may make detection analysis more challenging. Modifying existing services may interrupt their functionality or may enable services that are disabled or otherwise not commonly used.
Netsh Helper DLLPersistenceNetsh.exe (also referred to as Netshell) is a command-line scripting utility used to interact with the network configuration of a system. It contains functionality to add helper DLLs for extending functionality of the utility.TechNet Netsh The paths to registered netsh.exe helper DLLs are entered into the Windows Registry at HKLM\SOFTWARE\Microsoft\Netsh.

Adversaries can use netsh.exe with helper DLLs to proxy execution of arbitrary code in a persistent manner when netsh.exe is executed automatically with another Persistence technique or if other persistent software is present on the system that executes netsh.exe as part of its normal functionality. Examples include some VPN software that invoke netsh.exe.Demaske Netsh Persistence

Proof of concept code exists to load Cobalt Strike's payload using netsh.exe helper DLLs.Github Netsh Helper CS Beacon
New ServicePersistence
Privilege Escalation
When operating systems boot up, they can start programs or applications called services that perform background system functions.TechNet Services A service's configuration information, including the file path to the service's executable, is stored in the Windows Registry. Adversaries may install a new service that can be configured to execute at startup by using utilities to interact with services or by directly modifying the Registry. The service name may be disguised by using a name from a related operating system or benign software with Masquerading. Services may be created with administrator privileges but are executed under SYSTEM privileges, so an adversary may also use a service to escalate privileges from administrator to SYSTEM. Adversaries may also directly start services through Service Execution.
Office Application StartupPersistenceMicrosoft Office is a fairly common application suite on Windows-based operating systems within an enterprise network. There are multiple mechanisms that can be used with Office for persistence when an Office-based application is started.

Office Template Macros

Microsoft Office contains templates that are part of common Office applications and are used to customize styles. The base templates within the application are used each time an application starts.Microsoft Change Normal Template

Office Visual Basic for Applications (VBA) macrosMSDN VBA in Office can inserted into the base templated and used to execute code when the respective Office application starts in order to obtain persistence. Examples for both Word and Excel have been discovered and published. By default, Word has a Normal.dotm template created that can be modified to include a malicious macro. Excel does not have a template file created by default, but one can be added that will automatically be loaded.enigma0x3 normal.dotmHexacorn Office Template Macros

Word Normal.dotm location:C:\Users\(username)\AppData\Roaming\Microsoft\Templates\Normal.dotm

Excel Personal.xlsb location:C:\Users\(username)\AppData\Roaming\Microsoft\Excel\XLSTART\PERSONAL.XLSB

An adversary may need to enable macros to execute unrestricted depending on the system or enterprise security policy on use of macros.

Office Test

A Registry location was found that when a DLL reference was placed within it the corresponding DLL pointed to by the binary path would be executed every time an Office application is startedHexacorn Office Test

HKEY_CURRENT_USER\Software\Microsoft\Office test\Special\Perf

Add-ins

Office add-ins can be used to add functionality to Office programs.Microsoft Office Add-ins

Add-ins can also be used to obtain persistence because they can be set to execute code when an Office application starts. There are different types of add-ins that can be used by the various Office products; including Word/Excel add-in Libraries (WLL/XLL), VBA add-ins, Office Component Object Model (COM) add-ins, automation add-ins, VBA Editor (VBE), and Visual Studio Tools for Office (VSTO) add-ins.MRWLabs Office Persistence Add-ins
Path InterceptionPersistence
Privilege Escalation
Path interception occurs when an executable is placed in a specific path so that it is executed by an application instead of the intended target. One example of this was the use of a copy of cmd in the current working directory of a vulnerable application that loads a CMD or BAT file with the CreateProcess function.TechNet MS14-019

There are multiple distinct weaknesses or misconfigurations that adversaries may take advantage of when performing path interception: unquoted paths, path environment variable misconfigurations, and search order hijacking. The first vulnerability deals with full program paths, while the second and third occur when program paths are not specified. These techniques can be used for persistence if executables are called on a regular basis, as well as privilege escalation if intercepted executables are started by a higher privileged process.

Unquoted Paths

Service paths (stored in Windows Registry keys)Microsoft Subkey and shortcut paths are vulnerable to path interception if the path has one or more spaces and is not surrounded by quotation marks (e.g., C:\unsafe path with space\program.exe vs. "C:\safe path with space\program.exe").Baggett 2012 An adversary can place an executable in a higher level directory of the path, and Windows will resolve that executable instead of the intended executable. For example, if the path in a shortcut is C:\program files\myapp.exe, an adversary may create a program at C:\program.exe that will be run instead of the intended program.

PATH Environment Variable Misconfiguration

The PATH environment variable contains a list of directories. Certain methods of executing a program (namely using cmd.exe or the command-line) rely solely on the PATH environment variable to determine the locations that are searched for a program when the path for the program is not given. If any directories are listed in the PATH environment variable before the Windows directory, %SystemRoot%\system32 (e.g., C:\Windows\system32), a program may be placed in the preceding directory that is named the same as a Windows program (such as cmd, PowerShell, or Python), which will be executed when that command is executed from a script or command-line.

For example, if C:\example path precedes C:\Windows\system32 is in the PATH environment variable, a program that is named net.exe and placed in C:\example path will be called instead of the Windows system "net" when "net" is executed from the command-line.

Search Order Hijacking

Search order hijacking occurs when an adversary abuses the order in which Windows searches for programs that are not given a path. The search order differs depending on the method that is used to execute the program.Microsoft CreateProcessHill NT ShellMicrosoft WinExec However, it is common for Windows to search in the directory of the initiating program before searching through the Windows system directory. An adversary who finds a program vulnerable to search order hijacking (i.e., a program that does not specify the path to an executable) may take advantage of this vulnerability by creating a program named after the improperly specified program and placing it within the initiating program's directory.

For example, "example.exe" runs "cmd.exe" with the command-line argument net user. An adversary may place a program called "net.exe" within the same directory as example.exe, "net.exe" will be run instead of the Windows system utility net. In addition, if an adversary places a program called "net.com" in the same directory as "net.exe", then cmd.exe /C net user will execute "net.com" instead of "net.exe" due to the order of executable extensions defined under PATHEXT.MSDN Environment Property

Search order hijacking is also a common practice for hijacking DLL loads and is covered in DLL Search Order Hijacking.
Plist ModificationDefense Evasion
Persistence
Privilege Escalation
Property list (plist) files contain all of the information that macOS and OS X uses to configure applications and services. These files are UT-8 encoded and formatted like XML documents via a series of keys surrounded by < >. They detail when programs should execute, file paths to the executables, program arguments, required OS permissions, and many others. plists are located in certain locations depending on their purpose such as /Library/Preferences (which execute with elevated privileges) and ~/Library/Preferences (which execute with a user's privileges). Adversaries can modify these plist files to point to their own code, can use them to execute their code in the context of another user, bypass whitelisting procedures, or even use them as a persistence mechanismSofacy Komplex Trojan.
Rc.commonPersistenceDuring the boot process, macOS and Linux both execute source /etc/rc.common, which is a shell script containing various utility functions. This file also defines routines for processing command-line arguments and for gathering system settings, and is thus recommended to include in the start of Startup Item ScriptsStartup Items. In macOS and OS X, this is now a deprecated technique in favor of launch agents and launch daemons, but is currently still used. Adversaries can use the rc.common file as a way to hide code for persistence that will execute on each reboot as the root userMethods of Mac Malware Persistence.
Re-opened ApplicationsPersistenceStarting in Mac OS X 10.7 (Lion), users can specify certain applications to be re-opened when a user reboots their machine. While this is usually done via a Graphical User Interface (GUI) on an app-by-app basis, there are property list files (plist) that contain this information as well located at ~/Library/Preferences/com.apple.loginwindow.plist and ~/Library/Preferences/ByHost/com.apple.loginwindow.*.plist. An adversary can modify one of these files directly to include a link to their malicious executable to provide a persistence mechanism each time the user reboots their machineMethods of Mac Malware Persistence.
Redundant AccessDefense Evasion
Persistence
Adversaries may use more than one remote access tool with varying command and control protocols as a hedge against detection. If one type of tool is detected and blocked or removed as a response but the organization did not gain a full understanding of the adversary's tools and access, then the adversary will be able to retain access to the network. Adversaries may also attempt to gain access to Valid Accounts to use External Remote Services such as external VPNs as a way to maintain access despite interruptions to remote access tools deployed within a target network.Mandiant APT1 Use of a Web Shell is one such way to maintain access to a network through an externally accessible Web server.
Registry Run Keys / Start FolderPersistenceAdding an entry to the "run keys" in the Registry or startup folder will cause the program referenced to be executed when a user logs in.Microsoft Run Key The program will be executed under the context of the user and will have the account's associated permissions level. Adversaries can use these configuration locations to execute malware, such as remote access tools, to maintain persistence through system reboots. Adversaries may also use Masquerading to make the Registry entries look as if they are associated with legitimate programs.
Scheduled TaskExecution
Persistence
Privilege Escalation
Utilities such as at and schtasks, along with the Windows Task Scheduler, can be used to schedule programs or scripts to be executed at a date and time. The account used to create the task must be in the Administrators group on the local system. A task can also be scheduled on a remote system, provided the proper authentication is met to use RPC and file and printer sharing is turned on.TechNet Task Scheduler Security An adversary may use task scheduling to execute programs at system startup or on a scheduled basis for persistence, to conduct remote Execution as part of Lateral Movement, to gain SYSTEM privileges, or to run a process under the context of a specified account.
Security Support ProviderPersistenceWindows Security Support Provider (SSP) DLLs are loaded into the Local Security Authority (LSA) process at system start. Once loaded into the LSA, SSP DLLs have access to encrypted and plaintext passwords that are stored in Windows, such as any logged-on user's Domain password or smart card PINs. The SSP configuration is stored in two Registry keys: HKLM\SYSTEM\CurrentControlSet\Control\Lsa\Security Packages and HKLM\SYSTEM\CurrentControlSet\Control\Lsa\OSConfig\Security Packages. An adversary may modify these Registry keys to add new SSPs, which will be loaded the next time the system boots, or when the AddSecurityPackage Windows API function is called. Graeber 2014
Service Registry Permissions WeaknessPersistence
Privilege Escalation
Windows stores local service configuration information in the Registry under HKLM\SYSTEM\CurrentControlSet\Services. The information stored under a service's Registry keys can be manipulated to modify a service's execution parameters through tools such as the service controller, sc.exe, PowerShell, or Reg. Access to Registry keys is controlled through Access Control Lists and permissions.MSDN Registry Key Security If the permissions for users and groups are not properly set and allow access to the Registry keys for a service, then adversaries can change the service binPath/ImagePath to point to a different executable under their control. When the service starts or is restarted, then the adversary-controlled program will execute, allowing the adversary to gain persistence and/or privilege escalation to the account context the service is set to execute under (local/domain account, SYSTEM, LocalService, or NetworkService).
Shortcut ModificationPersistenceShortcuts or symbolic links are ways of referencing other files or programs that will be opened or executed when the shortcut is clicked or executed by a system startup process. Adversaries could use shortcuts to execute their tools for persistence. They may create a new shortcut as a means of indirection that may use Masquerading to look like a legitimate program. Adversaries could also edit the target path or entirely replace an existing shortcut so their tools will be executed instead of the intended legitimate program.
Startup ItemsPersistence
Privilege Escalation
Per Apple’s documentation, startup items execute during the final phase of the boot process and contain shell scripts or other executable files along with configuration information used by the system to determine the execution order for all startup itemsStartup Items. This is technically a deprecated version (superseded by Launch Daemons), and thus the appropriate folder, /Library/StartupItems isn’t guaranteed to exist on the system by default, but does appear to exist by default on macOS Sierra. A startup item is a directory whose executable and configuration property list (plist), StartupParameters.plist, reside in the top-level directory. An adversary can create the appropriate folders/files in the StartupItems directory to register their own persistence mechanismMethods of Mac Malware Persistence. Additionally, since StartupItems run during the bootup phase of macOS, they will run as root. If an adversary is able to modify an existing Startup Item, then they will be able to Privilege Escalate as well.
System FirmwarePersistenceThe BIOS (Basic Input/Output System) and The Unified Extensible Firmware Interface (UEFI) or Extensible Firmware Interface (EFI) are examples of system firmware that operate as the software interface between the operating system and hardware of a computer.Wikipedia BIOSWikipedia UEFIAbout UEFI System firmware like BIOS and (U)EFI underly the functionality of a computer and may be modified by an adversary to perform or assist in malicious activity. Capabilities exist to overwrite the system firmware, which may give sophisticated adversaries a means to install malicious firmware updates as a means of persistence on a system that may be difficult to detect.
TrapExecution
Persistence
The trap command allows programs and shells to specify commands that will be executed upon receiving interrupt signals. A common situation is a script allowing for graceful termination and handling of common keyboard interrupts like ctrl+c and ctrl+d. Adversaries can use this to register code to be executed when the shell encounters specific interrupts either to gain execution or as a persistence mechanism. Trap commands are of the following format trap 'command list' signals where "command list" will be executed when "signals" are received.
Valid AccountsDefense Evasion
Persistence
Privilege Escalation
Adversaries may steal the credentials of a specific user or service account using Credential Access techniques. Compromised credentials may be used to bypass access controls placed on various resources on hosts and within the network and may even be used for persistent access to remote systems. Compromised credentials may also grant an adversary increased privilege to specific systems or access to restricted areas of the network. Adversaries may choose not to use malware or tools in conjunction with the legitimate access those credentials provide to make it harder to detect their presence.

Adversaries may also create accounts, sometimes using pre-defined account names and passwords, as a means for persistence through backup access in case other means are unsuccessful.

The overlap of credentials and permissions across a network of systems is of concern because the adversary may be able to pivot across accounts and systems to reach a high level of access (i.e., domain or enterprise administrator) to bypass access controls set within the enterprise.TechNet Credential Theft
Web ShellPersistence
Privilege Escalation
A Web shell is a Web script that is placed on an openly accessible Web server to allow an adversary to use the Web server as a gateway into a network. A Web shell may provide a set of functions to execute or a command-line interface on the system that hosts the Web server. In addition to a server-side script, a Web shell may have a client interface program that is used to talk to the Web server (see, for example, China Chopper Web shell client).Lee 2013 Web shells may serve as Redundant Access or as a persistence mechanism in case an adversary's primary access methods are detected and removed.
Windows Management Instrumentation Event SubscriptionPersistenceWindows Management Instrumentation (WMI) can be used to install event filters, providers, consumers, and bindings that execute code when a defined event occurs. Adversaries may use the capabilities of WMI to subscribe to an event and execute arbitrary code when that event occurs, providing persistence on a system. Adversaries may attempt to evade detection of this technique by compiling WMI scripts.Dell WMI Persistence Examples of events that may be subscribed to are the wall clock time or the computer's uptime.Kazanciyan 2014 Several threat groups have reportedly used this technique to maintain persistence.Mandiant M-Trends 2015
Winlogon Helper DLLPersistenceWinlogon is a part of some Windows versions that performs actions at logon. In Windows systems prior to Windows Vista, a Registry key can be modified that causes Winlogon to load a DLL on startup. Adversaries may take advantage of this feature to load adversarial code at startup for persistence.