CVE-2026-44040

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-44040", "assignerOrgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "state": "PUBLISHED", "assignerShortName": "securin", "dateReserved": "2026-05-05T03:40:37.003Z", "datePublished": "2026-07-01T03:33:20.355Z", "dateUpdated": "2026-07-09T04:36:05.643Z"}, "containers": {"cna": {"title": "UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes", "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."}], "affected": [{"vendor": "uvnc", "product": "UltraVNC", "versions": [{"version": "0", "lessThanOrEqual": "1.8.2.2", "status": "affected", "versionType": "custom"}], "defaultStatus": "unaffected", "modules": ["winvnc", "vncviewer"]}], "problemTypes": [{"descriptions": [{"type": "CWE", "cweId": "CWE-338", "lang": "en", "description": "Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)"}]}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE", "baseScore": 4.8, "baseSeverity": "MEDIUM"}}], "references": [{"url": "https://uvnc.com/", "name": "UltraVNC project page", "tags": ["vendor-advisory"]}, {"url": "https://github.com/ultravnc/UltraVNC", "name": "UltraVNC source repository", "tags": ["product"]}, {"url": "https://www.securin.io/zero-days/cve-2026-44040-libc-rand-weak-rng-vnc-auth-challenge-ultravnc"}], "timeline": [{"time": "2026-06-02T00:00:00.000Z", "lang": "en", "value": "Vulnerability discovered during security audit"}, {"time": "2026-06-17T00:00:00.000Z", "lang": "en", "value": "Reported to vendor (coordinated disclosure)"}, {"time": "2026-09-15T00:00:00.000Z", "lang": "en", "value": "Planned public disclosure (90-day window)"}], "credits": [{"lang": "en", "value": "Arjun Basnet, Securin (arjun.basnet@securin.io)", "type": "finder"}], "source": {"discovery": "EXTERNAL", "advisory": "Securin Security Advisory \u2014 FINDING-001"}, "providerMetadata": {"orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "shortName": "securin", "dateUpdated": "2026-07-09T04:36:05.643Z"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-07-01T12:44:56.012420Z", "id": "CVE-2026-44040", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"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": "2026-07-01T12:45:04.706Z"}}]}}

{"dataType": "CVE_RECORD", "containers": {"adp": [{"title": "CISA ADP Vulnrichment", "metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2026-44040", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-01T12:44:56.012420Z"}}}], "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-07-01T12:45:00.742Z"}}], "cna": {"title": "UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes", "source": {"advisory": "Securin Security Advisory \u2014 FINDING-001", "discovery": "EXTERNAL"}, "credits": [{"lang": "en", "type": "finder", "value": "Arjun Basnet, Securin (arjun.basnet@securin.io)"}], "metrics": [{"format": "CVSS", "cvssV3_1": {"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"}, "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "affected": [{"vendor": "uvnc", "modules": ["winvnc", "vncviewer"], "product": "UltraVNC", "versions": [{"status": "affected", "version": "0", "versionType": "custom", "lessThanOrEqual": "1.8.2.2"}], "defaultStatus": "unaffected"}], "timeline": [{"lang": "en", "time": "2026-06-02T00:00:00.000Z", "value": "Vulnerability discovered during security audit"}, {"lang": "en", "time": "2026-06-17T00:00:00.000Z", "value": "Reported to vendor (coordinated disclosure)"}, {"lang": "en", "time": "2026-09-15T00:00:00.000Z", "value": "Planned public disclosure (90-day window)"}], "references": [{"url": "https://uvnc.com/", "name": "UltraVNC project page", "tags": ["vendor-advisory"]}, {"url": "https://github.com/ultravnc/UltraVNC", "name": "UltraVNC source repository", "tags": ["product"]}, {"url": "https://www.securin.io/zero-days/cve-2026-44040-libc-rand-weak-rng-vnc-auth-challenge-ultravnc"}], "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."}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-338", "description": "Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)"}]}], "providerMetadata": {"orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "shortName": "securin", "dateUpdated": "2026-07-09T04:36:05.643Z"}}}, "cveMetadata": {"cveId": "CVE-2026-44040", "state": "PUBLISHED", "dateUpdated": "2026-07-09T04:36:05.643Z", "dateReserved": "2026-05-05T03:40:37.003Z", "assignerOrgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "datePublished": "2026-07-01T03:33:20.355Z", "assignerShortName": "securin"}, "dataVersion": "5.2"}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "modules": ["winvnc", "vncviewer"], "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 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."}], "id": "CVE-2026-44040", "lastModified": "2026-10-25T17:10:00.197", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 4.8, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 2.2, "impactScore": 2.5, "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 2.5, "source": "nvd@nist.gov", "type": "Primary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-44040", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-07-01T12:44:56.012420Z", "version": "2.0.3"}}]}, "published": "2026-07-01T05:16:20.897", "references": [{"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "tags": ["Product"], "url": "https://github.com/ultravnc/UltraVNC"}, {"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "tags": ["Product", "Release Notes"], "url": "https://uvnc.com/"}, {"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "url": "https://www.securin.io/zero-days/cve-2026-44040-libc-rand-weak-rng-vnc-auth-challenge-ultravnc"}], "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-338"}], "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[0,1.8.2.2]"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "UltraVNC", "source": "cna", "vendor": "uvnc"}, "product": "ultravnc", "vendor": "uvnc"}], "created": "2026-07-01T09:00:14.844593+00:00", "updated": "2026-07-01T13:30:15.367104+00:00", "vendors": ["uvnc", "uvnc$PRODUCT$ultravnc"]}