GHSA-fjr4-x663-mwxc: GitPython Arbitrary File Overwrite Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-fjr4-x663-mwxc",
  "modified" : "2026-07-24T16:41:21Z",
  "published" : "2026-07-24T16:41:20Z",
  "aliases" : [ ],
  "summary" : "GitPython: Arbitrary file overwrite via git diff --output argument injection in Diffable.diff (key- and value-controlled)",
  "details" : "## Summary\n`Diffable.diff()` forwards `**kwargs` straight into `diff`/`diff_tree` with **no** `check_unsafe_options` guard. `Diffable` is mixed into `Commit`, `Tree`, `IndexFile`, and `Submodule`, giving a broad surface. `git diff --output=<path>` writes real patch content to an attacker-chosen path, enabling arbitrary file overwrite.\n\n## Root Cause\n`diff.py:188-283` builds and runs the diff command with no `check_unsafe_options` anywhere in the method (grep-confirmed). Additionally `diff.py:265` does `args.insert(0, other)`, placing the caller-supplied `other` ref BEFORE the `--` separator, so a value of `--output=/path` is parsed by git as an option — a value-only control path requiring no kwarg key.\n\n## Impact\nOverwrite/corrupt any file at process privilege with attacker-chosen path (e.g. `~/.ssh/authorized_keys`, configs, lockfiles). Content is real diff/patch bytes (attacker-influenced). Per the skill's rule, controlling WHICH file is overwritten = I:H regardless of content constraints.\n\n## Proof of Concept\n```python\n# Key-control:\ncommit.diff(other_commit, output='/home/app/.ssh/authorized_keys')   # victim overwritten with diff (105 bytes verified)\n# Value-control (attacker controls only the ref string):\ncommit.diff(other='--output=/home/app/.ssh/authorized_keys')          # 14-byte victim -> 146 bytes of diff-tree output\n```\n\n## Attack Chain\n1. Entry (value-control): `commit.diff(other=<user ref>)` with `other = \"--output=/home/app/.ssh/authorized_keys\"`. Guard: none in `Diffable.diff`. Bypass proof: no `check_unsafe_options` in the method body (grep); `other` inserted pre-`--` at diff.py:265.\n2. Sink: `git diff-tree <sha> --output=/home/app/.ssh/authorized_keys -r ...` -> git opens+truncates the target then writes diff content. Impact: overwrite/corrupt any file at process privilege (attacker chooses the path). Verified argv and victim overwrite live.\n\n## Bypass Evidence\nLive-verified on HEAD (tag 3.1.53): both key-control (`output=`) and value-control (`other='--output=...'`) overwrote a victim file with real diff-tree content; argv confirmed `['git','diff-tree','<sha>','--output=/victim','-r',...]`. This is the same value-control model GHSA-956x deemed fix-worthy for `iter_commits(rev='--output=')` — but `diff` is a distinct, unguarded sink NOT touched by that fix.\n\n## Affected Versions\n`<= 3.1.53`\n\n## Suggested Fix\nAdd `check_unsafe_options` to `Diffable.diff` (mirroring `iter_commits`/`archive`), and/or place `--end-of-options` before the `other` ref so it cannot be parsed as an option.\n\n---\nReported by **zx (Jace)** — GitHub: @manus-use",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "GitPython"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.1.54"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.1.53"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/gitpython-developers/GitPython/security/advisories/GHSA-fjr4-x663-mwxc"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gitpython-developers/GitPython/pull/2180"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gitpython-developers/GitPython/commit/1d51b891d7f236044a6aa17498ec682b63dad6e6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/gitpython-developers/GitPython"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gitpython-developers/GitPython/releases/tag/3.1.54"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-88" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-24T16:41:20Z",
    "nvd_published_at" : null
  }
}