GitPython CVE-2026-87818

The attacker must have low-privileged authenticated access (PR:L) to a service or application that exposes GitPython's high-level diff API and does not sanitize or restrict Git options passed by the caller. Specifically, the application must invoke GitPython's diff functionality in a way that forwards user-controlled arguments to the underlying git diff command without filtering --no-index or -I/--ignore-matching-lines. The target files must be readable by the OS user account under which the GitPython process runs. Exploitation is limited to single-line secret recovery per oracle session, making multi-line or binary file extraction significantly more complex. Deployments that do not expose diff functionality to untrusted authenticated users, or that run GitPython under a tightly sandboxed OS user, have materially reduced risk.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N) rates this at 7.1, reflecting low-complexity network exploitation requiring only low privilege, with high confidentiality impact and no integrity or availability impact. The PR:L requirement is the key mitigating factor: the attacker must already have authenticated, low-privileged access to a service exposing the GitPython diff API. The oracle attack is sophisticated and multi-step but fully deterministic, meaning even a mid-sized developer platform team in kielce running a GitLab-like CI/CD tool built atop GitPython should treat this as urgent for any deployment where users can trigger diff operations on server-side data. No KEV listing and no publicly confirmed POC exist at time of analysis, keeping real-world exploitation risk moderate; however, the technique is well-understood and the barrier to weaponization for a skilled attacker is low given that the GHSA advisory is public. EPSS data was not provided in the input, so exploitation probability cannot be quantified further.

An attacker with low-privileged access to a web-based code review or CI pipeline service built on GitPython crafts diff API requests injecting --no-index /dev/null /etc/app-secrets.conf to obtain diff output referencing the target file, then iterates with -I regex patterns to progressively narrow down character values in a secret API key stored in that file. After O(n × charset) requests, the full secret is recovered without the raw file content ever being directly echoed back.