Add folder enumeration signature for ransomware detection

[kevross33]

Implements a signature for folder enumeration, targeting user directories that are commonly accessed by ransomware or wipers.

LockBit

ZOVWiper

DynoWiper

[gemini-code-assist]

Summary of Changes

Hello @kevross33, 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 enhances the system's ability to detect early-stage ransomware and wiper attacks by implementing a new signature. This signature focuses on identifying malicious patterns of folder enumeration within critical user directories, thereby providing an earlier warning mechanism against potential data encryption or destruction attempts.

Highlights

• New Signature Added: A new Cuckoo signature named FolderEnumeration has been introduced to detect suspicious activity.
• Ransomware/Wiper Detection: This signature specifically targets the systematic searching of multiple user directories, a common behavior observed in the pre-encryption phases of ransomware and wiper malware.
• Targeted Directories and Threshold: The signature monitors access to common user directories such as Users, Documents, Desktop, Downloads, Music, Videos, Pictures, and AppData, triggering a detection if more than 10 unique folders matching these patterns are accessed.

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Changelog

• modules/signatures/windows/discovery_filesystem.py
  • Added a new signature for folder enumeration detection.

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[gemini-code-assist]

Code Review

This pull request introduces a new signature to detect folder enumeration, a common behavior of ransomware. A medium-severity Regular Expression Denial of Service (ReDoS) vulnerability was identified in the regex pattern. Additionally, improvements are suggested for making path matching case-insensitive for Windows, refining code style by removing a magic number and simplifying a return statement, and correcting an MBC classification code.

[gemini-code-assist]

The regular expression on this line is vulnerable to Regular Expression Denial of Service (ReDoS) due to the greedy quantifier .* which can lead to catastrophic backtracking. Additionally, Windows file paths are case-insensitive, and the current regex is case-sensitive, which could lead to missed detections on paths with different casing.

Suggested change

	pattern = r".*(Users|Documents|Desktop|Downloads|Music|Videos|Pictures|AppData).*\\\*.*"
	pattern = r"(?i).*?(Users|Documents|Desktop|Downloads|Music|Videos|Pictures|AppData).*\\\*.*"

[gemini-code-assist]

The MBC code B0002.001 corresponds to 'Block Interrupts', a debugger evasion technique. This appears to be incorrect for a signature that detects file and directory enumeration. Please update it to a more appropriate MBC code, or remove it if one doesn't exist.

[gemini-code-assist]

This if...return block can be simplified to a single, more concise return statement. Additionally, the threshold 10 is a magic number. It's recommended to define it as a class-level constant (e.g., TARGETED_FOLDERS_THRESHOLD = 10) to improve readability and maintainability.

        return len(targeted_folders) > 10