SIP Provider Modification for Defense Evasion

This detection rule identifies modifications to Subject Interface Package (SIP) providers, a critical component of the Windows cryptographic system responsible for validating file signatures. Attackers may attempt to subvert trust controls by modifying SIP providers, allowing them to bypass signature validation checks and potentially inject malicious code into trusted processes. This activity is a form of defense evasion, allowing unauthorized code execution. The rule focuses on detecting suspicious registry changes associated with SIP providers, while excluding known benign processes to minimize false positives. The rule is designed for data generated by Elastic Defend, but also supports third-party data sources like CrowdStrike, Microsoft Defender XDR, SentinelOne Cloud Funnel, and Sysmon. This activity is related to MITRE ATT&CK technique T1553.003 (SIP and Trust Provider Hijacking).

Attack Chain

1. The attacker gains initial access to the system through various means (e.g., phishing, exploitation of vulnerabilities).
2. The attacker escalates privileges to gain necessary permissions to modify the registry.
3. The attacker modifies the registry keys associated with SIP providers, specifically targeting CryptSIPDllPutSignedDataMsg and Trust\\FinalPolicy locations.
4. The attacker changes the Dll value within these registry keys to point to a malicious DLL.
5. The system, upon attempting to validate a file signature, loads the malicious DLL instead of the legitimate SIP provider.
6. The malicious DLL executes arbitrary code, potentially injecting it into other processes.
7. The attacker uses the injected code to further compromise the system or network.
8. The attacker achieves their final objective, such as data exfiltration, ransomware deployment, or establishing persistence.

Impact

Successful modification of SIP providers allows attackers to bypass signature validation checks, leading to the execution of unsigned or malicious code. This can compromise the integrity of the system, leading to data breaches, system instability, or further propagation of malware within the network. The impact can range from individual workstation compromise to widespread organizational damage, depending on the scope of the attack.

Recommendation

• Deploy the Sigma rule Detect SIP Provider Modification via Registry to your SIEM and tune it for your environment to detect suspicious registry modifications related to SIP providers.
• Enable Sysmon registry event logging to collect the necessary data for the Sigma rules above.
• Investigate any alerts generated by the rules, focusing on the process responsible for the registry change and the DLL being loaded, as described in the rule’s triage section.
• Implement application control policies to restrict the execution of unsigned or untrusted code.
• Monitor the registry paths listed in the Sigma rules for unexpected changes.