{"id":"CVE-2026-55199","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-55199","summary":"libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler","details":"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.","published":"2026-06-17T18:44:18.048Z","modified":"2026-08-26T18:27:58.169272313Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[],"fix":{"url":"https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4","label":"libssh2/libssh2@1762685"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55199.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55199"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler"},{"type":"REPORT","url":"https://github.com/libssh2/libssh2/pull/1864"},{"type":"FIX","url":"https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4"},{"type":"PACKAGE","url":"https://github.com/libssh2/libssh2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-26T18:27:58.169272313Z"}}