{"id":"CVE-2026-55199","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-55199","generatedAt":"2026-10-28T04:32:00.064Z","title":"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…","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.","published":"2026-06-17T20:17:29.000Z","lastModified":"2026-07-14T22:17:17.000Z","status":"Analyzed","sourceIdentifier":"disclosure@vulncheck.com","cvss":{"version":"4.0","score":8.2,"severity":"HIGH","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-835"],"affected":["libssh2/libssh2"],"epss":{"score":0.00918,"percentile":0.60056,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.92%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4","tags":["Patch"],"source":"disclosure@vulncheck.com"},{"url":"https://github.com/libssh2/libssh2/pull/1864","tags":["Patch"],"source":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler","tags":["Third Party Advisory"],"source":"disclosure@vulncheck.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-55199","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}