Add MalformedDllLoading signature for DLL checks

[kevross33]

Added a new signature class for detecting malformed DLL loading attempts, including checks for hex escapes and API strings in filenames.

Aside from cleaning it up I can't take credit as Gemini noticed it on a last past of malicious stuff in Pikabot (SHA256 ca5fb5814ec62c8f04936740aabe2664b3c7d036203afbd8425cd67cf1f4b79d) run and suggested it

[gemini-code-assist]

Summary of Changes

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This pull request enhances the system's malware detection capabilities by adding a new signature specifically designed to identify evasive techniques involving malformed DLL loading. The change allows for the recognition of suspicious patterns in DLL filenames that indicate an attempt to bypass standard analysis, thereby strengthening the overall security posture against sophisticated threats.

Highlights

• New Signature Added: Introduced a new signature, MalformedDllLoading, to detect attempts at loading DLLs with heavily malformed names or decoded API names.
• Detection Logic: The new signature identifies malformed DLL loading by checking for a high count of raw hex escapes (e.g., '\x') in filenames and the presence of known API strings within filenames, especially when the '.dll' extension is absent.
• Malware Evasion Detection: This signature targets errors in API hashing routines often used by malware, such as Pikabot, to evade detection, improving the system's ability to identify stealthy threats.

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Changelog

• modules/signatures/windows/dynamic_function_loading.py
  • Imported the 're' module for regular expression operations.
  • Added the 'MalformedDllLoading' class, a new signature for detecting suspicious DLL loading.

Activity

• No human activity has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request introduces a new signature, MalformedDllLoading, to detect attempts to load DLLs with malformed names. The implementation is sound and targets specific patterns like excessive hex escapes or the presence of API-like strings in DLL names. My review includes a few suggestions to improve code style, the correctness of the regular expression, and performance by moving a static list to a class attribute. These changes will enhance the readability and efficiency of the new signature.