{"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": "2026-07-01T12:45:04.706Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "shortName": "securin", "dateUpdated": "2026-07-01T03:33:20.355Z"}, "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"]}], "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"}}, "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"}}]}}

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