CVE-2026-55199 — libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler
libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a mali…
Published: 2026-06-17 · CVSS: 8.2 · CVSS 4.0
libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7