Update Stealc.yar

[bartblaze]

This should get rid of the FPs but not produce FNs.

[gemini-code-assist]

Summary of Changes

Hello @bartblaze, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the Stealc.yar YARA rule to reduce false positives. It achieves this by refining the detection logic to exclude legitimate files that might otherwise trigger the rule, specifically those importing certain DLLs, without compromising its ability to detect actual Stealc malware.

Highlights

• YARA Rule Refinement: The Stealc YARA rule has been updated to improve its accuracy by reducing false positives.
• PE Module Import: The pe module is now imported in Stealc.yar to enable Portable Executable (PE) file analysis within the YARA rules.
• False Positive Reduction Logic: New conditions have been added to the Stealc rule to prevent it from matching files that import tier0.dll or msdart.dll, which are likely legitimate applications.

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[gemini-code-assist]

Code Review

This pull request updates the Stealc YARA rule to reduce false positives by excluding files that import tier0.dll or msdart.dll. This change is logical and correctly implemented to avoid flagging legitimate software. My feedback includes one suggestion to add a comment explaining the purpose of this exclusion, which will improve the rule's long-term maintainability.

[gemini-code-assist]

For better maintainability, it would be helpful to add a comment explaining why tier0.dll and msdart.dll are being excluded. This provides context for future developers who might wonder about this condition and prevents accidental removal. The pull request description mentions this is to reduce false positives, which is great information to capture in the code itself.

        // Exclude common FPs from legitimate software (e.g., Valve Source Engine games).
        and not (pe.imports("tier0.dll") or pe.imports("msdart.dll"))

[kevoreilly]

I prefer to improve the signature patterns rather than add exclusions.

Please supply details and hashes for the FPs.

[bartblaze]

Agreed with this and had the same thought originally - although, that might mean getting rid of the $snippet1 string.. Example FP hashes:

03f891ce963ca916c865b91da8e9cd47dc97406c2cbc7d019964fe5b61d7343f
444ed825f744a8929d05f7900a8768e968e25489dfa0f73326833bc3bb5a55d9

Hope this helps,