CVE-2026-55199
CVE-2026-55199 · libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler
This page contains facts from public vulnerability sources. Check the original advisory before updating.
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.
CVSS 8.2 · High · EPSS 0.9% · Fix available
- Published
- Updated
Stack: system
Affected products and versions
libssh2
- Versions
- ≥ 0, ≤ 1.11.1: Affected (semver)
- 17626857d20b3c9a1addfa45979dadcee1cd84a4: Not affected (git)
No fix published
libssh2 Debian:13
- Versions
- 1.11.1-1
- Affected ranges
- ECOSYSTEM: < 1.11.1-1+deb13u1
Update to 1.11.1-1+deb13u1
libssh2 Debian:14
- Versions
- 1.11.1-1
- 1.11.1-2
- 1.11.1-3
- Affected ranges
- ECOSYSTEM: < 1.11.1-4
Update to 1.11.1-4
libssh2 Ubuntu:24.04:LTS
- Versions
- 1.11.0-2
- 1.11.0-3
- 1.11.0-4
- 1.11.0-4.1build1
- 1.11.0-4.1build2
- 1.11.0-4.1ubuntu0.24.04.1
- Affected ranges
- ECOSYSTEM: < 1.11.0-4.1ubuntu0.24.04.2
Update to 1.11.0-4.1ubuntu0.24.04.2
libssh2 Ubuntu:25.10
- Versions
- 1.11.1-1
- 1.11.1-1build1
- 1.11.1-1ubuntu0.25.10.1
- Affected ranges
- ECOSYSTEM: < 1.11.1-1ubuntu0.25.10.2
Update to 1.11.1-1ubuntu0.25.10.2
libssh2 Ubuntu:26.04:LTS
- Versions
- 1.11.1-1build1
- 1.11.1-1build2
- 1.11.1-1ubuntu0.26.04.1
- Affected ranges
- ECOSYSTEM: < 1.11.1-1ubuntu0.26.04.2
Update to 1.11.1-1ubuntu0.26.04.2