{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-66033", "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "state": "PUBLISHED", "assignerShortName": "VulnCheck", "dateReserved": "2026-07-23T20:45:17.816Z", "datePublished": "2026-07-24T16:35:28.607Z", "dateUpdated": "2026-07-28T01:06:25.504Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-07-28T01:06:25.504Z" }, "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. 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." } ], "tags": [ "x_open-source" ], "datePublic": "2026-07-23T00:00:00.000Z", "problemTypes": [ { "descriptions": [ { "lang": "en", "cweId": "CWE-191", "description": "Integer Underflow (Wrap or Wraparound)", "type": "CWE" }, { "lang": "en", "cweId": "CWE-125", "description": "Out-of-bounds Read", "type": "CWE" } ] } ], "affected": [ { "defaultStatus": "affected", "vendor": "libssh2", "product": "libssh2", "packageURL": "pkg:github/libssh2/libssh2", "repo": "https://github.com/libssh2/libssh2", "versions": [ { "status": "affected", "version": "0", "versionType": "semver", "lessThanOrEqual": "1.11.1" }, { "status": "unaffected", "version": "a2ed82d40964bbc0d64cd717aa0a5a892117d2e6", "versionType": "git" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:a:libssh2:libssh2:*:*:*:*:*:*:*:*", "versionEndIncluding": "1.11.1" } ] } ] } ], "metrics": [ { "format": "CVSS", "scenarios": [ { "lang": "en", "value": "GENERAL" } ], "cvssV4_0": { "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "subConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "subIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "version": "4.0", "baseSeverity": "HIGH", "baseScore": 8.7, "vectorString": "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" } }, { "format": "CVSS", "scenarios": [ { "lang": "en", "value": "GENERAL" } ], "cvssV3_1": { "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH", "version": "3.1", "baseSeverity": "HIGH", "baseScore": 7.5, "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H" } } ], "references": [ { "url": "https://github.com/libssh2/libssh2/pull/2401", "name": "Pull Request", "tags": [ "issue-tracking", "patch" ] }, { "url": "https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6", "name": "Patch Commit", "tags": [ "patch" ] }, { "url": "https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation", "tags": [ "third-party-advisory" ] } ], "credits": [ { "lang": "en", "value": "VladimirEliTokarev", "type": "finder" } ], "source": { "discovery": "UNKNOWN" }, "x_generator": { "engine": "vulncheck" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-07-27T16:15:25.211388Z", "id": "CVE-2026-66033", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-07-27T16:18:57.172Z" } } ] } }