PatchTheCVECVE-2026-44040: UltraVNC through 1.8.2.2 uses a cryptographically weak pseudo-random number generator to produce VNC authentic
CVE-2026-44040 is a medium-severity flaw (CVSS 4.8) affecting ultravnc. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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 att
Why this priority
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 4.8 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | High |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.4% (top 66%) |
| CISA exploited list | No |
| Weakness | CWE-338 |
| Published | 2026-07-01 |
| Last modified | 2026-10-25 |
Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-44040?
ultravnc: upgrade to newer than 1.8.2.2. Exact commands for each OS are on this page.
Is CVE-2026-44040 being exploited?
CVE-2026-44040 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-44040 affect?
CVE-2026-44040 affects ultravnc. Severity is medium (CVSS 4.8). 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()
How urgent is CVE-2026-44040?
Priority 30/100. Remotely exploitable, no login, no user action
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