CVE-2026-44040

MEDIUMNVD 6.54.8▼
EchelonGraph scoreMEDIUM confidence

Score 4.8 from GitHub Security Advisory published 2026-07-01. NVD baseline CVSS 6.5; sources differ by 1.7.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 4 sources updated this week
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 6.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
6.5
EG Score
4.8(medium)
EPSS
12.6%
KEV
Not listed

Published

July 1, 2026

Last Modified

July 2, 2026

Advisory Details (2)

Auto-updated Jul 1, 2026
No patch confirmed yet.
generic

Home - UltraVNC VNC OFFICIAL SITE, Remote Desktop Free Opensource

https://uvnc.com/
generic

GitHub - ultravnc/UltraVNC: 👁️ UltraVNC Server, UltraVNC Viewer, UltraVNC Repeater and UltraVNC SC | Official repository: https://github.com/ultravnc/UltraVNC · GitHub

https://github.com/ultravnc/UltraVNC

Vendor Advisories for CVE-2026-44040(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 20× in last 7d / 20× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-06 23:29 UTCEG score recompute
  2. 2026-07-06 23:29 UTCGHSA enrichment
  3. 2026-07-06 16:27 UTCEPSS rescore
  4. 2026-07-06 02:23 UTCEPSS rescore
  5. 2026-07-06 00:28 UTCEG score recompute
  6. 2026-07-06 00:28 UTCGHSA enrichment
  7. 2026-07-05 02:30 UTCEPSS rescore
  8. 2026-07-05 01:26 UTCEG score recompute
  9. 2026-07-05 01:26 UTCGHSA enrichment
  10. 2026-07-04 06:31 UTCEPSS rescore
  11. 2026-07-04 02:25 UTCEG score recompute
  12. 2026-07-04 02:25 UTCGHSA enrichment
  13. 2026-07-03 03:23 UTCEG score recompute
  14. 2026-07-03 03:23 UTCGHSA enrichment
  15. 2026-07-02 16:58 UTCNVD updateCVSS v3 → 6.5
  16. 2026-07-02 04:23 UTCEG score recompute
  17. 2026-07-02 04:22 UTCGHSA enrichment
  18. 2026-07-01 15:07 UTCEPSS rescore
  19. 2026-07-01 05:22 UTCEG score recompute
  20. 2026-07-01 05:20 UTCNVD updatefirst tracked

Frequently asked(5)

What is CVE-2026-44040?
CVE-2026-44040 is a medium vulnerability published on July 1, 2026. 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…
When was CVE-2026-44040 disclosed?
CVE-2026-44040 was first published in the National Vulnerability Database on July 1, 2026, with the most recent update on July 2, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-44040 actively exploited?
CVE-2026-44040 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 12.6% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-44040?
CVE-2026-44040 has a CVSS v3 base score of 6.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 4.8.
How do I remediate CVE-2026-44040?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-44040, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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