Vulnerability Description
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 Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Libssh2 | Libssh2 | <= 1.11.1 |
Related Weaknesses (CWE)
References
- https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84Patch
- https://github.com/libssh2/libssh2/pull/1864Patch
- https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-Third Party Advisory
FAQ
What is CVE-2026-55199?
CVE-2026-55199 is a vulnerability with a CVSS score of 5.9 (MEDIUM). 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 cau...
How severe is CVE-2026-55199?
CVE-2026-55199 has been rated MEDIUM with a CVSS base score of 5.9/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-55199?
Check the references section above for vendor advisories and patch information. Affected products include: Libssh2 Libssh2.