DLL Search Order Hijacking
Windows systems use a common method to look for required DLLs to load into a program.  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,  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.  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.   
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.
InvisiMole can be launched by using DLL search order hijacking in which the wrapper DLL is placed in the same folder as explorer.exe and loaded during startup into the Windows Explorer process instead of the legitimate library.
Prikormka uses DLL search order hijacking for persistence by saving itself as ntshrui.dll to the Windows directory so it will load before the legitimate ntshrui.dll saved in the System32 subdirectory.
Use auditing tools capable of detecting DLL search order hijacking opportunities on systems within an enterprise and correct them. Toolkits like the PowerSploit framework contain PowerUp modules that can be used to explore systems for DLL hijacking weaknesses.
Adversaries may use new DLLs to execute this technique. Identify and block potentially malicious software executed through search order hijacking by using application whitelisting solutions capable of blocking DLLs loaded by legitimate software.
|Restrict Library Loading||
Disallow loading of remote DLLs. This is included by default in Windows Server 2012+ and is available by patch for XP+ and Server 2003+. Path Algorithm
Enable Safe DLL Search Mode to force search for system DLLs in directories with greater restrictions (e.g.
The Safe DLL Search Mode can be enabled via Group Policy at Computer Configuration > [Policies] > Administrative Templates > MSS (Legacy): MSS: (SafeDllSearchMode) Enable Safe DLL search mode. The associated Windows Registry key for this is located at
Monitor file systems for moving, renaming, replacing, or modifying DLLs. Changes in the set of DLLs that are loaded by a process (compared with past behavior) that do not correlate with known software, patches, etc., are suspicious. Monitor DLLs loaded into a process and detect DLLs that have the same file name but abnormal paths. Modifications to or creation of .manifest and .local redirection files that do not correlate with software updates are suspicious.
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