RubyGems Symlink Path Traversal During Gem Extraction

Executive Summary

This vulnerability in RubyGems involves a failure to re-validate path containment after resolving symlinks during gem extraction. If a pre-existing symlink inside the destination directory points outside the extraction root, files can be written outside the intended directory, breaking the safety boundary. The fix checks the real path of the parent directory before writing and raises an error if it escapes the destination.

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Detection Guidance

To detect this vulnerability, check your RubyGems version with `gem --version`. If it is below 4.0.13, the system is vulnerable. Additionally, review gem extraction logs for `Gem::Package::PathError` exceptions which may indicate failed extraction attempts due to symlink escapes.

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Impact Analysis

An attacker could craft a malicious gem package that uses symlinks to write files outside the intended extraction directory. This could allow unauthorized file writes, potentially overwriting system files, installing malware, or gaining elevated privileges on the affected system.

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Compliance Impact

This vulnerability could lead to unauthorized data access or modification, violating confidentiality and integrity requirements in GDPR and HIPAA. It may result in non-compliance due to potential exposure of sensitive data or system compromise, leading to regulatory penalties or loss of trust.

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Mitigation Strategies

Upgrade RubyGems to version 4.0.13 or later using `gem update --system`. Avoid reusing directories for gem extraction and ensure no pre-existing symlinks point outside intended paths. Monitor extraction logs for errors.

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