{"id":"CVE-2026-76220","aliases":["GHSA-wvpp-8hx9-p66j","PYSEC-2026-3843"],"url":"https://o3.security/vulnerability/CVE-2026-76220","summary":"GitPython before 3.1.58 Command Execution via split_single_char_options","details":"## Summary\nThe `check_unsafe_options` guard can be bypassed on every guarded method (clone/clone_from, fetch/pull/push, ls_remote, iter_commits, blame, archive) by combining a single-character kwarg with `split_single_char_options=False`. The guard's candidate list omits the smuggled option, but `transform_kwarg` emits a JOINED `-n<value>` argv token that git parses as `--upload-pack=<cmd>`, yielding arbitrary command execution at the default `allow_unsafe_options=False`. This is an incomplete-fix bypass of commit `e8d0fbf7` (the fix for GHSA-r9mr-m37c-5fr3), which only emits value-derived candidates when `split_single_char_options` is True.\n\n## Root Cause\n`_option_candidates` derives value-token candidates only under `if len(key)==1 and split_single_char_options:` (cmd.py:1048, added by `e8d0fbf7`). With `split_single_char_options=False`, `_option_candidates([], {\"n\":\"utouch <cmd>;git-upload-pack\"})` returns only `['-n']` (not on the denylist), so the guard passes. But `transform_kwarg('n', value, split_single_char_options=False)` emits the JOINED token `-nutouch <cmd>;git-upload-pack` (cmd.py:1631). git clusters value-less short flags then parses `-u<cmd>` = `--upload-pack=<cmd>` → command execution. The hardened guard WOULD block the joined token if it saw it — the flaw is it never receives it.\n\n## Impact\nArbitrary OS command execution as the host process (via `--upload-pack`) at default `allow_unsafe_options=False`, affecting all guarded methods that forward kwargs. Precondition: the app forwards a user-controlled kwargs dict containing `split_single_char_options=False` plus a single-char key (same user-dict-forwarding model GHSA-r9mr-m37c-5fr3 accepts).\n\n## Proof of Concept\n```python\nfrom git import Repo\nRepo.clone_from(src, dst,\n    n=\"utouch /tmp/ACE;git-upload-pack\",\n    split_single_char_options=False)   # /tmp/ACE created -> ACE\n```\n\n## Attack Chain\n1. Entry: app forwards user kwargs to `Repo.clone_from(url, path, **kwargs)`: `{split_single_char_options: False, n: 'utouch /tmp/ACE;git-upload-pack'}`.\n2. Check: `check_unsafe_options(_option_candidates([], kwargs), unsafe_git_clone_options)`. Guard: denylist includes `--upload-pack`/`-u`. Bypass proof: `_option_candidates` yields only `['-n']` (value token skipped because `split=False`); guard never sees `-u`.\n3. Sink: `transform_kwarg` emits joined token (cmd.py:1631). argv (observed): `['git','clone','-v','-nutouch /tmp/ACE;git-upload-pack','--','<src>','<dst>']`.\n4. Impact: git clusters `-n` + `-u<cmd>` → runs upload-pack command → ACE.\n\n## Bypass Evidence\nIndependently reproduced (gate harness, default `allow_unsafe_options=False`): the `split=False` payload created the marker `VH05_GATE_ACE` (ACE); the clone returned normally (guard bypassed). Control: `n='--upload-pack=…'` (split default True) → `UnsafeOptionError: --upload-pack is not allowed`. Fix-commit read: `e8d0fbf7` extends candidates only under `if len(key)==1 and split_single_char_options:` — split=False skips value emission. Also confirmed the earlier clustering-parse fix (commit `56806080`) does not cover this because the guard only ever receives `['-n']`.\n\n## Affected Versions\n`GitPython <= 3.1.57` (code present verbatim on the latest release tag).\n\n## Suggested Fix\nMake `_option_candidates` emit value-derived candidates regardless of `split_single_char_options` (i.e. also for the joined `-n<value>` form), OR run `check_unsafe_options` over the fully-transformed argv rather than the reconstructed name-only candidate list.\n\n---\nReported by **zx (Jace)** — GitHub: @manus-use","published":"2026-08-19T14:02:04.108Z","modified":"2026-09-25T18:27:27.918325866Z","cvss":null,"epss":{"score":0.0057,"percentile":0.45766,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"gitpython","fixedVersion":"3.1.58"}],"fix":{"url":"https://github.com/gitpython-developers/GitPython/pull/2204","label":"gitpython-developers/GitPython#2204"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/76xxx/CVE-2026-76220.json"},{"type":"ADVISORY","url":"https://github.com/gitpython-developers/GitPython/security/advisories/GHSA-wvpp-8hx9-p66j"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-76220"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/gitpython-before-command-execution-via-split-single-char-options"},{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/pull/2204"},{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/commit/96a888f4d782cb2f80452148e48e60ce4af6d541"},{"type":"PACKAGE","url":"https://github.com/gitpython-developers/GitPython"},{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/releases/tag/3.1.58"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-25T18:27:27.918325866Z"}}