Security experts devised a stealth attack technique dubbed CIGslip that could be exploited by attackers to bypass Microsoft Code Integrity Guard (CIG)

Security researchers at Morphisec discovered a discovered stealth attack technique dubbed CIGslip that could be exploited by attackers to bypass Microsoft Code Integrity Guard (CIG) and inject malicious libraries into protected processes.

“Morphisec researchers Michael Gorelik and Andrey Diment have discovered CIGslip, a new method which can be exploited by attackers to bypass Microsoft’s Code Integrity Guard (CIG) and load malicious libraries into protected processes such as Microsoft Edge.” reads the analysis published by Morphisec.

“The new attack vector manipulates the way CIG works to circumvent its controls without any in-memory unsigned image codepage injection, a technique with destructive potential if becomes popular.”

CIGslip has a very low footprint on the targeted system and it is currently able to bypass almost all security mechanisms.

The researchers developed an attack POC that takes advantage of a non-CIG enabled process, that represents the majority of process on Windows, to enter a malicious code in any kind of DLL, including a malicious one.

Morphisec reported the issue to Microsoft, but according to the tech giant software giant responded that the technique is outside the scope of the for Mitigation Bypass and Bounty for Defense Terms.

According to Morphisec, the situation is dangerous for “Windows users [that] are vulnerable in multiple ways.”

“The attack POC takes advantage of a non-CIG enabled process, which is the most popular form of process on Windows, in order to sneak into a CIG-enabled target process, and uses it as an entry point to load any kind of DLL, including a malicious one,” continues the researchers.

The researchers explained that to compromise a targeted process, the attacker would have to perform a reflective memory based injection, but Microsoft added that generally this kind of attack can be detected and for this reason, it is out of the scope of bounty programs.

Researchers at Morphisec, however, are able to bypass Microsoft Code Integrity without any in-memory injection of unsigned image code pages, they demonstrated that it is possible to execute a non-protected CIG process that is used to inject back into the CIG protected process that launched it.

“Morphisec researchers identified a much easier method that breaks the CIG concept without any need for in-memory injection of unsigned image codepages.” continues the analysis. “The basic assumption is that we have the ability to execute a non-protected CIG process on disk. This assumption holds since there is no feasible way to protect all processes with CIG (e.g. Outlook would not load). Moreover, a CIG protected process may execute a non-CIG protected process, which will do the backward injection back into the CIG protected process.”

This means that an attacker would attempt to bypass the CIG verification in the backward injection when the section is created in the target process.

The attack is possible because section handlers that are managed by Kernel could be duplicated between processes.

“Since section handles are global objects managed by Kernel, handles could be duplicated between processes. Therefore, a section that correlated to a non-signed dll could be created within the context of the malicious process and then duplicated into the target process.” concluded the researchers.

“In-order to inject malicious dll (“non-signed”) into a target process, all we need to do is to hook the createsection method within the target process, so that it will not go down to Kernel and will return the duplicated section handle.”

Pierluigi Paganini

(Security Affairs – CIGslip, Microsoft Code Integrity Guard)

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