{"id":"CVE-2026-66033","state":"PUBLISHED","title":"libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation","description":"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.","publishedAt":"2026-07-24T16:35:28.607Z","updatedAt":"2026-07-28T01:06:25.504Z","severity":{"score":8.7,"label":"High","version":"4.0","vector":"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","source":"VulnCheck"},"assigner":"VulnCheck","products":["libssh2 libssh2"],"affected":[{"vendor":"libssh2","product":"libssh2","packageURL":"pkg:github/libssh2/libssh2","defaultStatus":"affected","versions":[{"version":"0","status":"affected","lessThanOrEqual":"1.11.1","versionType":"semver"},{"version":"a2ed82d40964bbc0d64cd717aa0a5a892117d2e6","status":"unaffected","versionType":"git"}],"repo":"https://github.com/libssh2/libssh2"}],"references":["https://github.com/libssh2/libssh2/pull/2401","https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6","https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation"],"weaknesses":["CWE-191","CWE-125"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/66xxx/CVE-2026-66033.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-66033","state":"PUBLISHED","datePublished":"2026-07-24T16:35:28.607Z","dateUpdated":"2026-07-28T01:06:25.504Z","assignerShortName":"VulnCheck","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateReserved":"2026-07-23T20:45:17.816Z"},"containers":{"cna":{"title":"libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation","descriptions":[{"lang":"en","value":"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. 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