{"id":"UBUNTU-CVE-2026-66034","details":"libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region.","modified":"2026-09-02T19:41:31.597064955Z","published":"2026-07-24T17:17:00Z","upstream":["CVE-2026-66034"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-66034"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-66034"},{"type":"REPORT","url":"https://github.com/libssh2/libssh2/pull/2202"},{"type":"REPORT","url":"https://www.vulncheck.com/advisories/libssh2-heap-out-of-bounds-read-via-publickey-subsystem"}],"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-2026-66034.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-2026-66034.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-2026-66034.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-2026-66034.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_version":"1.10.0-3","binary_name":"libssh2-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66034.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":"1.11.0-4.1ubuntu0.24.04.3"}]}],"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"],"ecosystem_specific":{"binaries":[{"binary_name":"libssh2-1t64","binary_version":"1.11.0-4.1ubuntu0.24.04.3"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-66034.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":"1.11.1-1ubuntu0.26.04.3"}]}],"versions":["1.11.1-1build1","1.11.1-1build2","1.11.1-1ubuntu0.26.04.1","1.11.1-1ubuntu0.26.04.2"],"ecosystem_specific":{"binaries":[{"binary_version":"1.11.1-1ubuntu0.26.04.3","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-2026-66034.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"}]}