{"api_version":"1","generated_at":"2026-07-03T23:46:03+00:00","cve":"CVE-2026-7830","urls":{"html":"https://cve.report/CVE-2026-7830","api":"https://cve.report/api/cve/CVE-2026-7830.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-7830","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-7830"},"summary":{"title":"UltraVNC MS-Logon II uses 64-bit Diffie-Hellman and seeded libc rand() enabling credential interception","description":"UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme (rfbUltraVNC_MsLogonIIAuth). In rfb/dh.cpp the Diffie-Hellman key exchange is performed with parameters that fit in an unsigned 64-bit integer (DH_MAX_BITS controls the prime size). A 64-bit DH key can be broken by Pollard's rho algorithm in under one second on current hardware. Additionally, the private exponent is generated by the rng() function, which multiplies three libc rand() values seeded from time(NULL). With approximately 31 bits of internal state and a time-based seed, the private exponent is recoverable in under a minute by a passive observer. A network attacker who can observe the MS-Logon II handshake (via sniffing, recording, or man-in-the-middle) can derive the shared DH key and decrypt the encapsulated username and password, resulting in full credential disclosure. This affects legacy MS-Logon II connections; MS-Logon III (X25519 + AES-256-GCM) is unaffected.","state":"PUBLISHED","assigner":"securin","published_at":"2026-07-01 05:16:24","updated_at":"2026-07-02 15:18:24"},"problem_types":["CWE-326","CWE-338","CWE-326 Inadequate Encryption Strength","CWE-338 Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)"],"metrics":[{"version":"3.1","source":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","type":"Secondary","score":"7.4","severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","baseScore":7.4,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"NONE"}},{"version":"3.1","source":"CNA","type":"CVSS","score":"7.4","severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","data":{"attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":7.4,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","version":"3.1"}}],"references":[{"url":"https://uvnc.com/","name":"https://uvnc.com/","refsource":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","tags":["Product","Release Notes"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/ultravnc/UltraVNC","name":"https://github.com/ultravnc/UltraVNC","refsource":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","tags":["Product"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-7830","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-7830","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"uvnc","product":"UltraVNC","version":"affected 1.8.2.2 custom","platforms":[]}],"timeline":[{"source":"CNA","time":"2026-06-02T00:00:00.000Z","lang":"en","value":"Vulnerability discovered during security audit"},{"source":"CNA","time":"2026-06-17T00:00:00.000Z","lang":"en","value":"Reported to vendor (coordinated disclosure)"},{"source":"CNA","time":"2026-09-15T00:00:00.000Z","lang":"en","value":"Planned public disclosure (90-day window)"}],"solutions":[],"workarounds":[],"exploits":[],"credits":[{"source":"CNA","value":"Arjun Basnet, Securin (arjun.basnet@securin.io)","lang":"en"}],"nvd_cpes":[{"cve_year":"2026","cve_id":"7830","vulnerable":"1","versionEndIncluding":"1.8.2.2","cpe1":"cpe","cpe2":"2.3","cpe3":"a","cpe4":"uvnc","cpe5":"ultravnc","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"}],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"7830","cve":"CVE-2026-7830","epss":"0.001830000","percentile":"0.080670000","score_date":"2026-07-02","updated_at":"2026-07-03 00:06:10"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"adp":[{"metrics":[{"other":{"content":{"id":"CVE-2026-7830","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","timestamp":"2026-07-01T13:13:10.627838Z","version":"2.0.3"},"type":"ssvc"}}],"providerMetadata":{"dateUpdated":"2026-07-01T13:13:23.590Z","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP"},"title":"CISA ADP Vulnrichment"}],"cna":{"affected":[{"defaultStatus":"unaffected","modules":["winvnc","ms-logon"],"product":"UltraVNC","vendor":"uvnc","versions":[{"lessThanOrEqual":"1.8.2.2","status":"affected","version":"0","versionType":"custom"}]}],"credits":[{"lang":"en","type":"finder","value":"Arjun Basnet, Securin (arjun.basnet@securin.io)"}],"descriptions":[{"lang":"en","value":"UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme (rfbUltraVNC_MsLogonIIAuth). 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In rfb/dh.cpp the Diffie-Hellman key exchange is performed with parameters that fit in an unsigned 64-bit integer (DH_MAX_BITS controls the prime size). A 64-bit DH key can be broken by Pollard's rho algorithm in under one second on current hardware. Additionally, the private exponent is generated by the rng() function, which multiplies three libc rand() values seeded from time(NULL). With approximately 31 bits of internal state and a time-based seed, the private exponent is recoverable in under a minute by a passive observer. A network attacker who can observe the MS-Logon II handshake (via sniffing, recording, or man-in-the-middle) can derive the shared DH key and decrypt the encapsulated username and password, resulting in full credential disclosure. This affects legacy MS-Logon II connections; MS-Logon III (X25519 + AES-256-GCM) is unaffected.","Type":"Description","Title":"UltraVNC MS-Logon II uses 64-bit Diffie-Hellman and seeded libc "}]}}}