{"id":"UBUNTU-CVE-2026-66035","details":"libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.","modified":"2026-09-03T23:04:21.352258554Z","published":"2026-07-24T17:17:00Z","related":["USN-8722-1"],"upstream":["CVE-2026-66035"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-66035"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-66035"},{"type":"REPORT","url":"https://github.com/libssh2/libssh2/pull/2198"},{"type":"REPORT","url":"https://www.vulncheck.com/advisories/libssh2-heap-buffer-overflow-via-etm-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_version":"1.4.3-2ubuntu0.2+esm3","binary_name":"libssh2-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66035.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_version":"1.5.0-2ubuntu0.1+esm2","binary_name":"libssh2-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66035.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-2026-66035.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-2026-66035.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-2026-66035.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-2026-66035.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-2026-66035.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"},{"type":"Ubuntu","score":"medium"}]}