{"id":"UBUNTU-CVE-2026-66033","details":"libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.","modified":"2026-09-03T23:04:20.831114053Z","published":"2026-07-24T17:17:00Z","related":["USN-8722-1"],"upstream":["CVE-2026-66033"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-66033"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-66033"},{"type":"REPORT","url":"https://github.com/libssh2/libssh2/pull/2401"},{"type":"REPORT","url":"https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-8722-1"}],"affected":[{"package":{"name":"libssh2","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.3-1","1.4.3-2","1.4.3-2ubuntu0.1","1.4.3-2ubuntu0.2","1.4.3-2ubuntu0.2+esm1","1.4.3-2ubuntu0.2+esm2","1.4.3-2ubuntu0.2+esm3"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1","binary_version":"1.4.3-2ubuntu0.2+esm3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66033.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=esm-apps%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.0-2","1.5.0-2ubuntu0.1","1.5.0-2ubuntu0.1+esm1","1.5.0-2ubuntu0.1+esm2"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1","binary_version":"1.5.0-2ubuntu0.1+esm2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66033.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:18.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=bionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.0-1","1.8.0-1ubuntu0.1"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1","binary_version":"1.8.0-1ubuntu0.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66033.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.0-2.1build1","1.8.0-2.1ubuntu0.1"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1","binary_version":"1.8.0-2.1ubuntu0.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66033.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.9.0-3","1.10.0-2","1.10.0-2build1","1.10.0-3"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1","binary_version":"1.10.0-3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66033.json"}},{"package":{"name":"libssh2","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/libssh2?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.11.0-4.1ubuntu0.24.04.4"}]}],"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","1.11.0-4.1ubuntu0.24.04.2","1.11.0-4.1ubuntu0.24.04.3"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_version":"1.11.0-4.1ubuntu0.24.04.4","binary_name":"libssh2-1t64"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66033.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":"1.11.1-1ubuntu0.26.04.4"}]}],"versions":["1.11.1-1build1","1.11.1-1build2","1.11.1-1ubuntu0.26.04.1","1.11.1-1ubuntu0.26.04.2","1.11.1-1ubuntu0.26.04.3"],"ecosystem_specific":{"binaries":[{"binary_version":"1.11.1-1ubuntu0.26.04.4","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-2026-66033.json"}}],"schema_version":"1.9.0","severity":[{"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:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"},{"type":"Ubuntu","score":"medium"}]}