{"schemaVersion":3,"id":"CVE-2026-44040","aliases":[],"status":"published","duplicateOf":null,"title":null,"description":"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.","dates":{"published":"2026-07-01T03:33:20.355Z","modified":"2026-07-09T04:36:05.643Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":6.5,"severity":"medium","version":"3.1","versionLabel":"v3.1","source":"NVD","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"CVE.org","score":4.8,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":6.5,"severity":"medium","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.00397,"percentile":0.32481,"severity":"low","asOf":"2026-10-20T00:00:00.000Z","change":{"pp":0,"baselineDate":"2026-09-20T00:00:00.000Z","baselineScore":0.00397},"history":[{"date":"2026-09-14T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-15T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-16T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-17T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-18T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00397,"percentile":0.32481}],"last30":[{"date":"2026-09-20T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00397,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","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