CVE-2026-53587: libgit2 Improper Input Validation

Vulnerability summary

CVE-2026-53587 is a high (CVSS 7.5) Improper Input Validation vulnerability in libgit2. EPSS estimates a 0.47% chance of exploitation in the next 30 days, higher than 39.6% of scored vulnerabilities.

Timeline

1. 20-08-2026
   PublishedVulnerability first disclosed.
2. 20-08-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.
• CWE-126Buffer Over-readThe product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.
• CWE-1284Improper Validation of Specified Quantity in InputThe product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.