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Report · CERT/CCAbout CVE-2026-128321Published

VU#644655: TightVNC and UltraVNC Viewer contains a heap-based buffer overflow

Source CERT/CC

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Authoritative record:CVE-2026-128321· High

Not known to be exploited · fixed in 1.8.2.8 : patch UltraVNC soon.

Data as of 13 Nov 2026, 01:25 UTC

Severity
High

Rated High by Threat Radar's AI analysis · CVSS not yet scored by NVD

Thin evidence

One scorer or none
Patch
Available – fixed in 1.8.2.8

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 13 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Affected software

ProductAffectedFixed in
UltraVNCUltraVNCAffected
  • >=1.8.2.4 <=1.8.2.6
Fixed in–
Glavsoft (TightVNC)TightVNCAffected
  • >=1.3.10 <=1.3.10
Fixed in–
GitHubultravnc/ultravncpkg:github/ultravnc/ultravncOther threatsAffected
  • >=1.8.2.4 <=1.8.2.6
  • =1.3.10
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

UltraVNC users should upgrade to version 1.8.2.8 or later (e.g., 1.8.3.1) to obtain the fix for this vulnerability. TightVNC users should replace the affected 1.3.10 Windows viewer with a maintained version or an alternative remote desktop solution that addresses the issue. Until a fixed viewer is deployed, restrict VNC connections to trusted servers only, understanding that this does not protect against a compromised trusted server.

Description

A heap-based buffer overflow vulnerability exists in the Tight JPEG decoding component of TightVNC Windows Viewer 1.3.10 and affected UltraVNC Windows Viewers. A malicious VNC server can send a specially crafted screen update that triggers memory corruption by overflowing a heap buffer during JPEG decompression. This can crash the viewer and interrupt remote desktop sessions. Although arbitrary code execution is possible in theory, only denial of service was demonstrated during testing. UltraVNC has fixed this issue in version 1.8.2.8 and later. TightVNC has not provided a fix, so users should replace affected viewers or restrict connections to trusted servers.

References

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