Out-of-bounds Read in Libgit2

CVE-2026-53587

libgit2 is a portable C implementation of the Git core methods provided as a linkable library with a solid API, allowing to build Git functionality into your application. Prior to 1.8.6 and 1.9.5, libgit2 performs a fixed-size strncmp in set_data in src/libgit2/transports/smart_pkt.c without first verifying that the smart-protocol pkt-line capability buffer contains 14 bytes. A malicious Git server can make bytes after the pkt-line complete object-format=, causing format_str to advance beyond the pkt-line and the following memchr length calculation to underflow. The resulting heap out-of-bounds walk can crash a client during the first refs-advertisement packet over HTTP, HTTPS, SSH, or the Git protocol. This issue is fixed in versions 1.8.6 and 1.9.5.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.005 (38.5th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 38th percentile — 38.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-53587: held from 0.005 to 0.005.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

  • Libgit2 — versions < 1.8.6, >= 1.9.0, < 1.9.5

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-53587?
CVE-2026-53587 is a high-severity vulnerability in Libgit2, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2026-08-20.
How severe is CVE-2026-53587?
High severity. CVSS v3 base score is 7.5 out of 10.
Is CVE-2026-53587 known to be exploited?
1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.