# CVE-2026-128321: Tight JPEG decoding in TightVNC and UltraVNC viewers contains a heap-based buffer overflow vulnerability

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- UltraVNC / UltraVNC: ≥ 1.8.2.4; ≤ 1.8.2.6 (affected, custom). Source: CNA: certcc
- Glavsoft (TightVNC) / TightVNC: ≥ 1.3.10; ≤ 1.3.10 (affected, custom). Source: CNA: certcc

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-122

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://www.tightvnc.com/ (CNA: certcc)

- https://github.com/ultravnc/ultravnc (CNA: certcc)

- https://www.kb.cert.org/vuls/id/644655 (ADP: CVE)

## Provenance

- CNA: certcc: https://www.cve.org/CVERecord?id=CVE-2026-128321; retrieved 2026-11-13; source updated 2026-11-13

Revision: 2ee830f84eaa98f2a397fb55549da073e7abe4fee2c13581765006291e317ce9

Canonical: https://y2.dev/cve/CVE-2026-128321

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