Attack and Defense insights on weakness due to unquoted Service Path

Adversaries may execute their own malicious payloads by hijacking vulnerable file path references. Adversaries can take advantage of paths that lack surrounding quotations by placing an executable in a higher level directory within the path, so that Windows will choose the adversary's executable to launch.

Service paths  and shortcut paths may also be 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").  (stored in Windows Registry keys) 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.  

This technique 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.

The words are exactly as per mitre  Hijack Execution Flow: Path Interception by Unquoted Path.The purpose of this blog is to understand how the process looks like on Attack side, specifically to highlight which is the crucial area the defender can use to spot the attacker. 

Lets review the attack side first

Auditing the system to know the options attacker has on the system

The Output will be similar to do this

Now lets see how the attacker uses the unquoted service path weakness in the system

Attack VS Defense : 

Now lets have a top level understanding of where the defense team has opportunity to spot the attacker. on the above mentioned process.

Attacker : Attacker loaded powersploit module after execution policy bypass in powershell

Defender: Defender can monitor powershell commands executed where execution policy bypass may be a low severity indicator , however invoke expression pointing towards github page is definite suspicious behavior.

Attacker : Attacker created services.exe and renamed it to filezilla.exe after placing them in relavent path and restarted the machine to have the persistence

Defender : All the actions performed here are suspicious behavior,if sufficient monitoring is in place on windows telemetry

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.

Defense Strategy

Auditing

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

Execution Prevention

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 C: and system directories, such as C:\Windows\, to reduce places where malicious files could be placed for execution. Require that all executables be placed in write-protected directories.