BREW-SNAKEMAKE-CVE-2026-87818 (PYSEC-2026-3983)
Vulnerability from osv_homebrew – Published: 2026-09-18 18:39 – Updated: 2026-10-01 11:43 – Source websiteSummary
GitPython 3.1.59 blocks a previously available local-file read path through unsafe git diff options such as -O/--orderfile.
However, the high-level diff API still permits --no-index with the default allow_unsafe_options=False.
--no-index changes the semantics of the paths arguments: instead of repository-relative pathspecs, Git interprets them as arbitrary filesystem paths.
When combined with the still-allowed -I/--ignore-matching-lines option, this creates a content-dependent Boolean oracle over a caller-selected local file.
This was reproduced against the published GitPython 3.1.59 wheel.
The original unsafe-option path is blocked in 3.1.59, while this alternate path remains reachable without setting allow_unsafe_options=True.
Details
Confirmed API surface:
repo.index.diff( None, no_index=True, I=pattern, paths=[baseline_path, target_path], create_patch=True, )
The relevant behavior is:
- --no-index makes the two values supplied via paths filesystem operands rather than repository pathspecs.
- -I/--ignore-matching-lines makes Git's result depend on whether the supplied regular expression matches the relevant file content.
- GitPython exposes the resulting bit through distinguishable behavior:
- matching condition: normal return with an empty DiffIndex
- non-matching condition: GitCommandError with exit status 1
An 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.
The issue was confirmed with the default allow_unsafe_options=False.
The behavior does not require the caller to explicitly opt into GitPython's unsafe-option mode.
Verified intended security boundary:
- GitPython 3.1.58 accepts the earlier -O/--orderfile local-file input path.
- GitPython 3.1.59 rejects that same path with UnsafeOptionError.
- GitPython 3.1.59 still permits the --no-index alternate path described above.
This 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.
PoC
A minimal reproducer, controlled extraction demonstrator, proof matrix, and proposed remediation are included in the attached package.
gitpython-3159-maintainer-evidence.zip
The minimal reproducer creates only temporary researcher-controlled files and demonstrates the following predicate:
correct prefix -> normal GitPython return incorrect prefix -> GitCommandError(status=1)
In 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.
Result: 3/3 recovered.
The 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.
Controls were also tested:
- normal repository-scoped diff: no secret disclosure
- same outside paths without --no-index: no arbitrary-filesystem interpretation
- deliberately incorrect predicate: status 1 as expected
Suggested remediation is to classify --no-index as unsafe for the high-level diff API unless the caller explicitly sets allow_unsafe_options=True.
Impact
Potential impact is disclosure of local files readable by the process running GitPython.
Exploitation requires an embedding application to allow an attacker to influence:
- the relevant diff options,
- both path operands, and
- repeated requests while exposing a distinguishable success/error result.
The 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.
Confirmed affected release: GitPython 3.1.59.
{
"affected": [
{
"ecosystem_specific": {
"fix": "bump",
"range_state": "fixed",
"resource": "gitpython",
"resource_purl": "pkg:pypi/gitpython@3.1.62",
"upstream_fixed_in": "3.1.60"
},
"package": {
"ecosystem": "Homebrew",
"name": "snakemake",
"purl": "pkg:brew/snakemake"
},
"ranges": [
{
"events": [
{
"introduced": "9.25.2"
},
{
"fixed": "9.26.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"confidence": "high",
"source": "matched",
"strategy": "registry",
"upstream_evidence": [
{
"ecosystem": "PyPI",
"key": "pkg:pypi/gitpython@3.1.62",
"name": "gitpython",
"resource": "gitpython",
"strategy": "registry",
"subject_version": "3.1.62"
}
]
},
"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\u0027s 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\u0027s 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.",
"id": "BREW-snakemake-CVE-2026-87818",
"modified": "2026-10-01T11:43:20Z",
"published": "2026-09-18T18:39:20Z",
"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"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
}
],
"summary": "GitPython: --no-index bypasses diff unsafe-option protections and enables a blind local-file content oracle",
"upstream": [
"PYSEC-2026-3983",
"CVE-2026-87818",
"GHSA-whh4-5q6c-9v3x"
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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