{"id":"UBUNTU-CVE-2026-55199","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.","modified":"2026-09-05T06:15:18.062924580Z","published":"2026-06-17T20:17:00Z","related":["USN-8486-1"],"upstream":["CVE-2026-55199"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-55199"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-55199"},{"type":"REPORT","url":"https://github.com/libssh2/libssh2/pull/1864"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-8486-1"}],"affected":[{"package":{"name":"libssh2","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.11.0-4.1ubuntu0.24.04.2"}]}],"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"],"ecosystem_specific":{"binaries":[{"binary_version":"1.11.0-4.1ubuntu0.24.04.2","binary_name":"libssh2-1t64"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55199.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.11.1-1ubuntu0.25.10.2"}]}],"versions":["1.11.1-1","1.11.1-1build1","1.11.1-1ubuntu0.25.10.1"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1t64","binary_version":"1.11.1-1ubuntu0.25.10.2"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55199.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.11.1-1ubuntu0.26.04.2"}]}],"versions":["1.11.1-1build1","1.11.1-1build2","1.11.1-1ubuntu0.26.04.1"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_version":"1.11.1-1ubuntu0.26.04.2","binary_name":"libssh2-1t64"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55199.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"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"},{"type":"Ubuntu","score":"medium"}]}