Arbitrary file write via unvalidated Git refs
Published Sep 4, 2026 · Updated Sep 8, 2026
Argument injection in Cyanheads Git MCP Server 2.15.3 and earlier allows remote attackers to write files via crafted Git refs. The git_log, git_diff, and git_show handlers pass unvalidated ref or object strings into Git's argument vector before the option terminator, so leading-dash values such as --output= are parsed as Git options. Attackers must be able to submit MCP tool arguments; successful exploitation overwrites or creates files only at paths writable by the server process.
Summary
What happened
Argument injection in Cyanheads Git MCP Server 2.15.3 and earlier allows remote attackers to write files via crafted Git refs. The git_log, git_diff, and git_show handlers pass unvalidated ref or object strings into Git's argument vector before the option terminator, so leading-dash values such as --output= are parsed as Git options. Attackers must be able to submit MCP tool arguments; successful exploitation overwrites or creates files only at paths writable by the server process.
The record
- CVE
- CVE-2026-85626
- Published
- Sep 4, 2026
- Updated
- Sep 8, 2026
- Vendor
- Cyanheads
- Product
- Git MCP Server
- Classifications
- CWE-88, T1565.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 4, 2026CVE publishedPublication date reported by the CVE source.
- Sep 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <=2.15.3
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- git_log --output arbitrary-file-write proof of conceptfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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