CVE-2026-87818

GitPython 3.1.59 fails to restrict the --no-index option in its high-level diff API, so arguments injected into diff invocations (CWE-88) can cause Git to treat arbitrary local filesystem paths as repository operands, exposing file contents to an attacker. The flaw is triggered when an application passes attacker-controlled arguments into that diff API, for example a service that lets users supply refs, paths, or diff flags. By pairing --no-index with -I/--ignore-matching-lines, the attacker gains a content-dependent Boolean oracle: success or error responses differ depending on whether a guessed string matches a line in a local file, allowing repeated queries to recover single-line secrets. Any deployment running GitPython 3.1.59 whose high-level diff API is reachable with user-influenced arguments is affected, while other uses of the library are not impacted. No exploitation has been reported: the issue is not in CISA KEV, no public proof-of-concept is known, and it carries a CVSS 4.0 score of 7.1 (High).

What to do: Audit applications for calls to GitPython's high-level diff API that pass user-controlled arguments, and strip or whitelist injected diff options such as --no-index and -I/--ignore-matching-lines. Upgrade to a patched GitPython release when one becomes available, since the advisory names 3.1.59 as affected but does not specify a fixed version. As defense in depth, limit the filesystem and secret access of accounts running GitPython-based services so arbitrary file reads yield little of value.