CVE-2026-7838

HIGHPre-NVD 8.88.8—
EchelonGraph scoreHIGH confidence

Score 8.8 from GitHub Security Advisory (severity: HIGH) published 2026-07-01. a secondary CVSS source baseline 8.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
8.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 8.8Exploit: NoneExposed: 0

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

UltraVNC viewer through 1.8.2.2 contains an integer overflow leading to a heap buffer overflow in the RFB protocol failure-response parsing path. In vncviewer/ClientConnection.cpp, the 4-byte network-supplied reasonLen field (type CARD32) is passed as reasonLen+1 to CheckBufferSize(). Because both operands are unsigned 32-bit, a reasonLen of 0xFFFFFFFF overflows to 0, causing CheckBufferSize to allocate only 256 bytes. The subsequent ReadString(m_netbuf, reasonLen) call then performs ReadExact for the original 4 GiB length into that 256-byte heap buffer. This overflow is reachable via rfbConnFailed (auth-scheme negotiation) and rfbVncAuthFailed (post-handshake) message types without successful authentication. A malicious VNC server, or any man-in-the-middle on the RFB stream, can trigger this condition when the victim viewer connects, potentially resulting in remote code execution as the user running the viewer. The crash was confirmed with AddressSanitizer on a portable reproduction harness (heap-buffer-overflow WRITE at offset 256).

CVSS v3
8.8
EG Score
8.8(high)
EPSS
63.1%
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-2026-7838(1)

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

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 35× in last 7d / 35× 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. 2026-07-07 06:20 UTCEG score recompute
  2. 2026-07-07 06:20 UTCGHSA enrichment
  3. 2026-07-06 18:16 UTCEG score recompute
  4. 2026-07-06 18:16 UTCGHSA enrichment
  5. 2026-07-06 16:27 UTCEPSS rescore
  6. 2026-07-06 16:27 UTCEPSS rescore
  7. 2026-07-06 06:11 UTCEG score recompute
  8. 2026-07-06 06:11 UTCGHSA enrichment
  9. 2026-07-06 02:23 UTCEPSS rescore
  10. 2026-07-06 02:23 UTCEPSS rescore
  11. 2026-07-05 18:02 UTCEG score recompute
  12. 2026-07-05 18:02 UTCGHSA enrichment
  13. 2026-07-05 05:58 UTCEG score recompute
  14. 2026-07-05 05:58 UTCGHSA enrichment
  15. 2026-07-05 02:31 UTCEPSS rescore
  16. 2026-07-05 02:30 UTCEPSS rescore
  17. 2026-07-04 17:54 UTCEG score recompute
  18. 2026-07-04 17:54 UTCGHSA enrichment
  19. 2026-07-04 06:31 UTCEPSS rescore
  20. 2026-07-04 06:31 UTCEPSS rescore
  21. 2026-07-04 05:49 UTCEG score recompute
  22. 2026-07-04 05:48 UTCGHSA enrichment
  23. 2026-07-03 17:41 UTCEG score recompute
  24. 2026-07-03 17:41 UTCGHSA enrichment
  25. 2026-07-03 05:37 UTCEG score recompute
Show 10 more
  1. 2026-07-03 05:37 UTCGHSA enrichment
  2. 2026-07-02 17:33 UTCEG score recompute
  3. 2026-07-02 17:32 UTCGHSA enrichment
  4. 2026-07-02 05:28 UTCEG score recompute
  5. 2026-07-02 05:28 UTCGHSA enrichment
  6. 2026-07-01 17:24 UTCEG score recompute
  7. 2026-07-01 17:24 UTCGHSA enrichment
  8. 2026-07-01 15:07 UTCEPSS rescore
  9. 2026-07-01 05:21 UTCEG score recompute
  10. 2026-07-01 05:20 UTCNVD updatefirst tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-7838?
CVE-2026-7838 is a high vulnerability published on July 1, 2026. UltraVNC viewer through 1.8.2.2 contains an integer overflow leading to a heap buffer overflow in the RFB protocol failure-response parsing path. In vncviewer/ClientConnection.cpp, the 4-byte network-supplied reasonLen field (type CARD32) is passed as reasonLen+1 to CheckBufferSize(). Because both…
When was CVE-2026-7838 disclosed?
CVE-2026-7838 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-2026-7838 actively exploited?
CVE-2026-7838 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 63.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-7838?
CVE-2026-7838 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2026-7838?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-7838, 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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