Hijack Execution Flow: Path Interception by Search Order Hijacking
Other sub-techniques of Hijack Execution Flow (11)
Adversaries may execute their own malicious payloads by hijacking the search order used to load other programs. Because some programs do not call other programs using the full path, adversaries may place their own file in the directory where the calling program is located, causing the operating system to launch their malicious software at the request of the calling program.
Search order hijacking occurs when an adversary abuses the order in which Windows searches for programs that are not given a path. Unlike DLL Search Order Hijacking, the search order differs depending on the method that is used to execute the program.    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. 
Search order hijacking is also a common practice for hijacking DLL loads and is covered in DLL Search Order Hijacking.
Find and eliminate path interception weaknesses in program configuration files, scripts, the PATH environment variable, services, and in shortcuts by surrounding PATH variables with quotation marks when functions allow for them. Be aware of the search order Windows uses for executing or loading binaries and use fully qualified paths wherever appropriate.
Clean up old Windows Registry keys when software is uninstalled to avoid keys with no associated legitimate binaries. Periodically search for and correct or report path interception weaknesses on systems that may have been introduced using custom or available tools that report software using insecure path configurations.
Adversaries will likely need to place new binaries in locations to be executed through this weakness. Identify and block potentially malicious software executed path interception by using application control tools, like Windows Defender Application Control, AppLocker, or Software Restriction Policies where appropriate.
|Restrict File and Directory Permissions||
Ensure that proper permissions and directory access control are set to deny users the ability to write files to the top-level directory
Monitor file creation for files named after partial directories and in locations that may be searched for common processes through the environment variable, or otherwise should not be user writable. Monitor the executing process for process executable paths that are named for partial directories. Monitor file creation for programs that are named after Windows system programs or programs commonly executed without a path (such as "findstr," "net," and "python"). If this activity occurs outside of known administration activity, upgrades, installations, or patches, then it may be suspicious.
Data and events should not be viewed in isolation, but as part of a chain of behavior that could lead to other activities, such as network connections made for Command and Control, learning details about the environment through Discovery, and Lateral Movement.
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