{"id":"GHSA-whh4-5q6c-9v3x","summary":"GitPython: --no-index bypasses diff unsafe-option protections and enables a blind local-file content oracle","details":"### Summary\n\nGitPython 3.1.59 blocks a previously available local-file read path through unsafe git diff options such as -O/--orderfile.\n\nHowever, the high-level diff API still permits --no-index with the default allow_unsafe_options=False.\n\n--no-index changes the semantics of the paths arguments: instead of repository-relative pathspecs, Git interprets them as arbitrary filesystem paths.\n\nWhen combined with the still-allowed -I/--ignore-matching-lines option, this creates a content-dependent Boolean oracle over a caller-selected local file.\n\nThis was reproduced against the published GitPython 3.1.59 wheel.\n\nThe original unsafe-option path is blocked in 3.1.59, while this alternate path remains reachable without setting allow_unsafe_options=True.\n\n### Details\n\nConfirmed API surface:\n\nrepo.index.diff(\n    None,\n    no_index=True,\n    I=pattern,\n    paths=[baseline_path, target_path],\n    create_patch=True,\n)\n\nThe relevant behavior is:\n\n1. --no-index makes the two values supplied via paths filesystem operands rather than repository pathspecs.\n2. -I/--ignore-matching-lines makes Git's result depend on whether the supplied regular expression matches the relevant file content.\n3. GitPython exposes the resulting bit through distinguishable behavior:\n   - matching condition: normal return with an empty DiffIndex\n   - non-matching condition: GitCommandError with exit status 1\n\nAn application that forwards attacker-influenced diff options and paths and exposes the success/error distinction can therefore be queried repeatedly to recover a guessable local single-line secret.\n\nThe issue was confirmed with the default allow_unsafe_options=False.\n\nThe behavior does not require the caller to explicitly opt into GitPython's unsafe-option mode.\n\nVerified intended security boundary:\n\n- GitPython 3.1.58 accepts the earlier -O/--orderfile local-file input path.\n- GitPython 3.1.59 rejects that same path with UnsafeOptionError.\n- GitPython 3.1.59 still permits the --no-index alternate path described above.\n\nThis appears to be an alternate route to the same local-file confidentiality property that the 3.1.59 diff option hardening is intended to protect.\n\n### PoC\n\nA minimal reproducer, controlled extraction demonstrator, proof matrix, and proposed remediation are included in the attached package.\n\n[gitpython-3159-maintainer-evidence.zip](https://github.com/user-attachments/files/31123571/gitpython-3159-maintainer-evidence.zip)\n\n\nThe minimal reproducer creates only temporary researcher-controlled files and demonstrates the following predicate:\n\ncorrect prefix   -\u003e normal GitPython return\nincorrect prefix -\u003e GitCommandError(status=1)\n\nIn the controlled extraction test, I generated three independent random single-line values and recovered all three exactly through repeated calls to the GitPython high-level API.\n\nResult: 3/3 recovered.\n\nThe extraction harness also installs a Python audit hook that rejects direct Python open() access to the target file during the oracle phase. The content-dependent read is therefore performed by the child git process invoked through GitPython rather than by the reproduction script directly.\n\nControls were also tested:\n\n- normal repository-scoped diff: no secret disclosure\n- same outside paths without --no-index: no arbitrary-filesystem interpretation\n- deliberately incorrect predicate: status 1 as expected\n\nSuggested remediation is to classify --no-index as unsafe for the high-level diff API unless the caller explicitly sets allow_unsafe_options=True.\n\n### Impact\n\nPotential impact is disclosure of local files readable by the process running GitPython.\n\nExploitation requires an embedding application to allow an attacker to influence:\n\n1. the relevant diff options,\n2. both path operands, and\n3. repeated requests while exposing a distinguishable success/error result.\n\nThe demonstrated attack is a blind content oracle rather than a one-request in-band file read. It is particularly applicable to short or structured single-line secrets where the target path and approximate value format are known or guessable.\n\nConfirmed affected release: GitPython 3.1.59.","aliases":["CVE-2026-87818"],"modified":"2026-10-01T17:26:00.195974026Z","published":"2026-09-30T23:28:40Z","database_specific":{"github_reviewed_at":"2026-09-30T23:28:40Z","nvd_published_at":null,"cwe_ids":["CWE-200","CWE-88"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/security/advisories/GHSA-whh4-5q6c-9v3x"},{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/pull/2217"},{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/commit/09f2cf383a992d1af697364569e9f384748c1bd8"},{"type":"PACKAGE","url":"https://github.com/gitpython-developers/GitPython"},{"type":"WEB","url":"https://github.com/gitpython-developers/GitPython/releases/tag/3.1.60"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/gitpython/PYSEC-2026-3983.yaml"},{"type":"WEB","url":"https://www.vulncheck.com/advisories/gitpython-3.1.59-local-file-content-oracle-via-no-index"}],"affected":[{"package":{"name":"gitpython","ecosystem":"PyPI","purl":"pkg:pypi/gitpython"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.1.59"},{"fixed":"3.1.60"}]}],"versions":["3.1.59"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-whh4-5q6c-9v3x/GHSA-whh4-5q6c-9v3x.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"}]}