High [CVE-2026-53587] Denial of Service due to heap out-of-bounds read from malicious Git server

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.

A flaw was found in libgit2. A fixed-size string comparison in the `set_data` function within `transports/smart_pkt.c` does not adequately verify the size of a network packet buffer.

A remote attacker, operating a malicious Git server, can send a specially crafted packet-line capability buffer. This can lead to a heap out-of-bounds read, causing the client application to crash and resulting in a Denial of Service (DoS).

Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-125.