---
id: CVE-2026-128321
title: >-
  Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based
  buffer overflow vulnerability
summary: >-
  Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based
  buffer overflow because an attacker-controlled framebuffer rectangle width is
  not validated against a fixed-size decoding buffer. A malicious VNC server can
  cause…
severity: none
cwe:
  - CWE-122
vendor: UltraVNC
product: UltraVNC
affected:
  - UltraVNC >= 1.8.2.4 <= 1.8.2.6
  - TightVNC >= 1.3.10 <= 1.3.10
published: '2026-11-13'
updated: '2026-11-13'
sourceUpdated: '2026-11-13T02:05:51.969Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-128321'
references:
  - url: 'https://www.tightvnc.com/'
  - url: 'https://github.com/ultravnc/ultravnc'
tags:
  - cve.org
ingestedAt: '2026-11-13T01:19:02.081Z'
---

## Overview

Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based buffer overflow because an attacker-controlled framebuffer rectangle width is not validated against a fixed-size decoding buffer. A malicious VNC server can cause an out-of-bounds heap write when a user connects, resulting in application crash and potentially other memory-corruption impacts.

## Affected

- `UltraVNC >= 1.8.2.4 <= 1.8.2.6`
- `TightVNC >= 1.3.10 <= 1.3.10`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.