GitPython: --no-index bypasses diff unsafe-option protections and enables a blind local-file content oracle

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Why it is Yellow

• CVSS 6.5 medium
• On your watchlist: PyPI

Affected packages

References

• https://github.com/advisories/GHSA-whh4-5q6c-9v3x
• https://github.com/gitpython-developers/GitPython/security/advisories/GHSA-whh4-5q6c-9v3x
• https://github.com/gitpython-developers/GitPython/pull/2217
• https://github.com/gitpython-developers/GitPython/commit/09f2cf383a992d1af697364569e9f384748c1bd8
• https://github.com/gitpython-developers/GitPython/releases/tag/3.1.60
• https://github.com/pypa/advisory-database/tree/main/vulns/gitpython/PYSEC-2026-3983.yaml
• https://www.vulncheck.com/advisories/gitpython-3.1.59-local-file-content-oracle-via-no-index
• https://github.com/advisories/GHSA-whh4-5q6c-9v3x

Original description

### Summary 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: 1. --no-index makes the two values supplied via paths filesystem operands rather than repository pathspecs. 2. -I/--ignore-matching-lines makes Git's result depend on whether the supplied regular expression matches the relevant file content. 3. 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](https://github.com/user-attachments/files/31123571/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: 1. the relevant diff options, 2. both path operands, and 3. 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.