CVE-2026-128321VulnerabilityPublished 13 Nov 2026

TightVNC · Tight JPEG Decoding

Source GCVE Database

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Authoritative record:CVE-2026-128321· High

Not known to be exploited.

Data as of 13 Nov 2026, 04:40 UTC

Severity

High

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

Thin evidence

One scorer or none

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-2v2r-xq5w-26rm

What to do

Affected software

Product	Affected	Fixed in
UltraVNCUltraVNC	Affected >=1.8.2.4 <=1.8.2.6	Fixed in–
Glavsoft (TightVNC)TightVNC	Affected >=1.3.10 <=1.3.10	Fixed in–
GitHubultravnc/ultravnc`pkg:github/ultravnc/ultravnc`Other threats	Affected >=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

Until a fix is available, users should avoid connecting to untrusted or unknown VNC servers to mitigate risk.

Description

A heap-based buffer overflow vulnerability exists in the Tight JPEG decoding component of TightVNC and UltraVNC viewers. This occurs because the width of an attacker-controlled framebuffer rectangle is not validated against a fixed-size decoding buffer. A malicious VNC server can exploit this flaw to cause an out-of-bounds heap write when a user connects, potentially leading to application crashes and other memory corruption effects.

Impact

A malicious VNC server can exploit this vulnerability to cause an application crash or potentially other memory corruption issues in the TightVNC or UltraVNC viewer on the client side. This could disrupt user sessions or potentially be leveraged for further exploitation depending on the memory corruption consequences.

Summary

The vulnerability in TightVNC and UltraVNC viewers arises from improper validation of the framebuffer rectangle width during Tight JPEG decoding. Specifically, the decoding buffer has a fixed size, but the width value provided by the VNC server is attacker-controlled and unchecked, allowing a heap-based buffer overflow. This can be triggered remotely by connecting to a malicious VNC server, resulting in out-of-bounds heap writes that may cause crashes or other memory corruption impacts.

References

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