{"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": "2026-07-25T10:30:08.332Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-07-25T10:30:08.332Z"}, "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"}]}], "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"}}}}

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{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,1.11.1]"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "code_commit", "value": "a2ed82d40964bbc0d64cd717aa0a5a892117d2e6"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "libssh2", "source": "cna", "vendor": "libssh2"}, "product": "libssh2", "vendor": "libssh2"}], "created": "2026-07-24T22:45:17.097790+00:00", "updated": "2026-07-24T22:45:17.097816+00:00", "vendors": ["libssh2", "libssh2$PRODUCT$libssh2"]}