DOS Drive Letter Prefix Validation Bypass in Dulwich

Executive Summary

This is a Path Traversal vulnerability in the Dulwich Git library affecting Windows systems. It fails to block DOS drive letter prefixes like 'C:' in Git tree paths. When a malicious repository contains an entry named 'C:', the checkout logic allows writing files outside the intended worktree directory. This happens because Windows path handling discards the root path if the second argument contains an absolute drive letter. Attackers can exploit this to write arbitrary files on a victim's Windows machine, potentially leading to Remote Code Execution.

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Detection Guidance

Check the installed version of Dulwich with pip show dulwich. If it is below 1.2.9, the system is vulnerable. Inspect Git repositories for tree entries containing drive letters like 'C:' or other DOS paths. Monitor for unexpected file writes outside worktree directories.

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Impact Analysis

If you use a vulnerable version of Dulwich on Windows, an attacker could craft a malicious Git repository that writes files outside the intended directory. This could allow them to overwrite system files, install malware, or execute arbitrary code on your machine. Attack vectors include Git config poisoning, persistence via Startup folder, or compromising CI/CD runners. Even Linux users could be targeted if they share repositories with Windows users.

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Compliance Impact

This vulnerability could lead to unauthorized file access or modification, violating data integrity and confidentiality requirements in GDPR and HIPAA. If exploited, it may result in unauthorized data exposure, system compromise, or data tampering, which are direct violations of these regulations. Organizations using vulnerable versions may face compliance failures, legal penalties, and reputational damage.

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Mitigation Strategies

Upgrade Dulwich to version 1.2.9 or later immediately. Avoid cloning or interacting with untrusted Git repositories. Implement strict input validation for Git tree paths. Monitor file system changes for suspicious writes outside expected directories.

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