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The plugin installation process inside Claude Code and Claude Desktop allows developers to download and integrate third-party extensions to enhance coding workflows. To enforce security and code integrity, the system relies on hash pinning, where a specific 40-character Git commit SHA is checked out to guarantee that only pre-reviewed code gets executed. However, during the checkout operation, the underlying mechanism invoked `git checkout
This missing post-checkout validation created an exploitable flaw when interacting with remote Git servers. An attacker maintaining a plugin repository could create a remote Git branch named identically to the exact 40-character commit SHA string. Because Git prioritizes branch names during git checkout, the operation silently checked out the attacker’s malicious branch tip rather than the safe, reviewed commit SHA.
As a result, the user’s application accepted the repository content without throwing any warnings or hash mismatch errors, rendering the hash-pinning mechanism completely ineffective. Because installed plugins run directly within the workstation environment inheriting full developer privileges, this logic bypass allowed arbitrary untrusted code execution on the local host.
DailyCVE Form:
Platform: Claude Code Desktop
Version: Prior to 2.1.179
Vulnerability: Hash Pin Bypass
Severity: High Severity
date: October 9 2026
Prediction: Already Patched Fixed
What Undercode Say:
The vulnerability demonstrates how Git reference resolution ambiguities can break critical software supply chain controls. Developers often treat commit SHAs as immutable identifiers, assuming that checking out a SHA is inherently safe. However, without explicitly verifying that `HEAD` resolves to the target commit object rather than a branch or ref, client-side tools remain vulnerable to spoofed upstream branch names.
Verify currently installed Claude Code version claude --version Update Claude Code to the fixed version npm update -g @anthropic-ai/claude-code Verify resolved HEAD against expected SHA after git checkout git rev-parse HEAD
Exploit:
1. Create a repository containing malicious plugin code.
- Identify the target 40-character SHA string (e.g.,
a1b2c3d4e5f678901234567890abcdef12345678) pinned by users. - Create a Git branch named identically to that 40-character SHA:
git checkout -b a1b2c3d4e5f678901234567890abcdef12345678 git add malicious_plugin.js git commit -m "PoC Malicious Payload" git push origin a1b2c3d4e5f678901234567890abcdef12345678
- When a user runs the plugin installation command with the pinned SHA, `git checkout` resolves to the attacker’s branch tip instead of the pinned commit.
Protection:
Update Claude Code: Upgrade to version `2.1.179` or later, which strictly verifies post-checkout `HEAD` values.
Auto-Updates: Ensure standard auto-update functionality remains enabled in Claude Code and Claude Desktop.
Audit Extensions: Review third-party plugin sources and remove untrusted repository references.
Impact:
Successful exploitation allows remote attackers to bypass commit hash verification and execute arbitrary code on developer machines using the user’s local operating system permissions.
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Sources:
Reported By: github.com
Extra Source Hub:
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