CVE-2026-7840

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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "modules": ["repeater"], "product": "UltraVNC", "vendor": "uvnc", "versions": [{"lessThanOrEqual": "1.8.2.2", "status": "affected", "version": "0", "versionType": "custom"}]}], "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*", "matchCriteriaId": "593F7EC1-0922-4652-817A-7D57A0F1210D", "versionEndIncluding": "1.8.2.2", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP administration server. The functions wi_senderr() and wi_replyhdr() in repeater/webgui/webutils.c write the caller-supplied HTTP request URI into a fixed 1000-byte global buffer (hdrbuf) via unchecked sprintf calls. The HTTP receive buffer accepts URIs up to approximately 150 KB (WI_RXBUFSIZE = 153600), so an unauthenticated attacker who can reach the repeater HTTP port (default TCP 80) can overflow hdrbuf by at least 500 bytes with a single HTTP request containing a URI of 1500 bytes or longer, corrupting adjacent .bss-segment globals. The overflow occurs before any authentication check, making it reachable without credentials. A remote, unauthenticated attacker can achieve arbitrary code execution on the host running the repeater."}, {"lang": "es", "value": "El repetidor UltraVNC hasta la versi\u00f3n 1.8.2.2 contiene un desbordamiento de b\u00fafer global en su servidor de administraci\u00f3n HTTP incrustado. Las funciones wi_senderr() y wi_replyhdr() en repeater/webgui/webutils.c escriben la URI de solicitud HTTP proporcionada por el llamador en un b\u00fafer global fijo de 1000 bytes (hdrbuf) a trav\u00e9s de llamadas sprintf sin verificar. El b\u00fafer de recepci\u00f3n HTTP acepta URIs de hasta aproximadamente 150 KB (WI_RXBUFSIZE = 153600), por lo que un atacante no autenticado que puede alcanzar el puerto HTTP del repetidor (TCP 80 por defecto) puede desbordar hdrbuf en al menos 500 bytes con una \u00fanica solicitud HTTP que contenga una URI de 1500 bytes o m\u00e1s, corrompiendo variables globales adyacentes del segmento .bss. El desbordamiento ocurre antes de cualquier verificaci\u00f3n de autenticaci\u00f3n, haci\u00e9ndolo alcanzable sin credenciales. Un atacante remoto no autenticado puede lograr la ejecuci\u00f3n de c\u00f3digo arbitrario en el host que ejecuta el repetidor."}], "id": "CVE-2026-7840", "lastModified": "2026-10-25T17:10:00.197", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 9.8, "baseSeverity": "CRITICAL", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 5.9, "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "type": "Secondary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 9.3, "baseSeverity": "CRITICAL", "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:H/VI:H/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": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-7840", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2026-07-01T12:33:40.320112Z", "version": "2.0.3"}}]}, "published": "2026-07-01T05:16:24.820", "references": [{"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "tags": ["Product"], "url": "https://github.com/ultravnc/UltraVNC"}, {"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "tags": ["Product"], "url": "https://uvnc.com/"}, {"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "url": "https://www.securin.io/zero-days/cve-2026-7840-pre-auth-global-buffer-overflow-repeater-http-admin-ultravnc"}], "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-787"}], "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "type": "Secondary"}]}

{}

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