CVE-2026-66033

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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."}, {"lang": "es", "value": "libssh2 hasta 1.11.1, corregido en el commit a2ed82d, contiene una vulnerabilidad de desbordamiento negativo de enteros (integer underflow) pre-autenticaci\u00f3n en la funci\u00f3n ssh2_cipher_crypt() en src/openssl.c que permite a un servidor SSH malicioso bloquear cualquier cliente que se conecte al negociar cifrados AES-GCM durante el handshake. Los atacantes pueden explotar el desbordamiento negativo en la expresi\u00f3n que calcula blocksize menos aadlen menos la longitud de la etiqueta de autenticaci\u00f3n para desencadenar una lectura fuera de l\u00edmites (out-of-bounds read) y una llamada a memcpy con un argumento de longitud cercano a SIZE_MAX, causando el bloqueo inmediato del proceso antes de que ocurra cualquier autenticaci\u00f3n."}], "id": "CVE-2026-66033", "lastModified": "2026-11-08T16:10:00.183", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "disclosure@vulncheck.com", "type": "Secondary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 8.7, "baseSeverity": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "disclosure@vulncheck.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-66033", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-07-27T16:15:25.211388Z", "version": "2.0.3"}}]}, "published": "2026-07-24T17:17:35.263", "references": [{"source": "disclosure@vulncheck.com", "tags": ["Patch"], "url": "https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6"}, {"source": "disclosure@vulncheck.com", "tags": ["Issue Tracking", "Patch"], "url": "https://github.com/libssh2/libssh2/pull/2401"}, {"source": "disclosure@vulncheck.com", "tags": ["Patch", "Third Party Advisory"], "url": "https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation"}], "sourceIdentifier": "disclosure@vulncheck.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-125"}, {"lang": "en", "value": "CWE-191"}], "source": "disclosure@vulncheck.com", "type": "Secondary"}]}

{"affected_release": [{"advisory": "RHSA-2026:46927", "cpe": "cpe:/a:redhat:hummingbird:1", "impact": "important", "package": "libssh2-main-1.11.1-10.2.hum1", "product_name": "Red Hat Hardened Images", "release_date": "2026-07-27T00:00:00Z"}], "bugzilla": {"description": "libssh2: libssh2: Denial of Service via integer underflow in AES-GCM cipher negotiation", "id": "2506853", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2506853"}, "csaw": false, "cvss3": {"cvss3_base_score": "6.5", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H", "status": "verified"}, "cwe": "CWE-125", "details": ["A flaw was found in libssh2. A pre-authentication integer underflow vulnerability exists in the `ssh2_cipher_crypt()` function when negotiating AES-GCM ciphers during the handshake. A malicious SSH server can exploit this to trigger an out-of-bounds read and a memory copy operation with an extremely large length argument, leading to an immediate client process crash. This vulnerability results in a Denial of Service (DoS) for any connecting client."], "mitigation": {"lang": "en:us", "value": "To mitigate the vulnerability, developers or administrators must configure the specific applications utilizing libssh2 to explicitly exclude AES-GCM from their preferred cipher lists."}, "name": "CVE-2026-66033", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "libssh2", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Affected", "package_name": "libssh2", "product_name": "Red Hat Enterprise Linux 7"}], "public_date": "2026-07-24T16:35:28Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-66033\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-66033\nhttps://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6\nhttps://github.com/libssh2/libssh2/pull/2401\nhttps://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation"], "statement": "This Moderate impact flaw in libssh2 allows a malicious SSH server to trigger a client-side denial of service. The vulnerability, an integer underflow during AES-GCM cipher negotiation, can cause a connecting client to crash before authentication. Exploitation requires the client to connect to a specially crafted, untrusted SSH server.", "threat_severity": "Moderate"}

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