CVE-2026-128321

Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based buffer overflow vulnerability

Description

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.

Key facts

Published: 13 Nov 2026
Last changed: 13 Nov 2026
Assigned by: certcc
EPSS: 0.203% likely to be exploited in the next 30 days, higher than 10.362% of CVEs (scores for 15 Nov 2026)

Historical context and remediation

This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.

No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.

No explicit remediation statement is available on this page yet. Consult the original record and vendor references before choosing a fix.

Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.

Read the original CVE record.

Affected products

Vendor	Product	Versions
UltraVNC	UltraVNC	1.8.2.4 up to and including 1.8.2.6 (affected)
Glavsoft (TightVNC)	TightVNC	1.3.10 up to and including 1.3.10 (affected)

Timeline

13 Nov 2026 Published