CVE-2026-44040

{"id": "CVE-2026-44040", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-44040", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-01T12:44:56.012420Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.8, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "HIGH", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "LOW"}, "impactScore": 2.5, "exploitabilityScore": 2.2}, {"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 6.5, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "LOW"}, "impactScore": 2.5, "exploitabilityScore": 3.9}]}, "affected": [{"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "affectedData": [{"vendor": "uvnc", "modules": ["winvnc", "vncviewer"], "product": "UltraVNC", "versions": [{"status": "affected", "version": "0", "versionType": "custom", "lessThanOrEqual": "1.8.2.2"}], "defaultStatus": "unaffected"}]}], "published": "2026-07-01T05:16:20.897", "references": [{"url": "https://github.com/ultravnc/UltraVNC", "tags": ["Product"], "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}, {"url": "https://uvnc.com/", "tags": ["Product", "Release Notes"], "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}, {"url": "https://www.securin.io/zero-days/cve-2026-44040-libc-rand-weak-rng-vnc-auth-challenge-ultravnc", "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}], "vulnStatus": "Modified", "weaknesses": [{"type": "Secondary", "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "description": [{"lang": "en", "value": "CWE-338"}]}], "descriptions": [{"lang": "en", "value": "UltraVNC through 1.8.2.2 uses a cryptographically weak pseudo-random number generator to produce VNC authentication challenge bytes. In rfb/vncauth.c:119-129, the vncRandomBytes() function seeds libc rand() with time(0) + getpid() + rand() and generates a 16-byte challenge. The combined seed space is approximately 31 bits (libc rand() internal state) and is entirely determined by publicly-observable values (wall-clock time and process ID). An attacker who can observe the authentication exchange can enumerate the seed space and predict the challenge within seconds, enabling forgery or offline brute-forcing of responses. Note: on Windows, the active code path may use vncEncryptBytes2.cpp which calls CryptGenRandom; reachability on shipped Windows binaries requires compile-graph verification and is under investigation."}, {"lang": "es", "value": "UltraVNC hasta la versi\u00f3n 1.8.2.2 utiliza un generador de n\u00fameros pseudoaleatorios criptogr\u00e1ficamente d\u00e9bil para producir bytes de desaf\u00edo de autenticaci\u00f3n VNC. En rfb/vncauth.c:119-129, la funci\u00f3n vncRandomBytes() inicializa libc rand() con time(0) + getpid() + rand() y genera un desaf\u00edo de 16 bytes. El espacio de semillas combinado es de aproximadamente 31 bits (estado interno de libc rand()) y est\u00e1 completamente determinado por valores p\u00fablicamente observables (tiempo de reloj de pared y ID de proceso). Un atacante que puede observar el intercambio de autenticaci\u00f3n puede enumerar el espacio de semillas y predecir el desaf\u00edo en segundos, lo que permite la falsificaci\u00f3n o el ataque de fuerza bruta sin conexi\u00f3n de las respuestas. Nota: en Windows, la ruta de c\u00f3digo activa puede usar vncEncryptBytes2.cpp que llama a CryptGenRandom; la accesibilidad en los binarios de Windows distribuidos requiere verificaci\u00f3n del grafo de compilaci\u00f3n y est\u00e1 bajo investigaci\u00f3n."}], "lastModified": "2026-10-25T17:10:00.197", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "593F7EC1-0922-4652-817A-7D57A0F1210D", "versionEndIncluding": "1.8.2.2"}], "operator": "OR"}]}], "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}