Is CVE-2026-7831 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-7831 being exploited in the wild.

How severe is CVE-2026-7831?

High severity, with a CVSS score of 7.6, published 1 July 2026.

Which products and versions are affected?

UltraVNC Viewer through 1.8.2.2.

Is there a fix for CVE-2026-7831?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-7831 attacked?

It is attacked over the network, in a network appliance.

Am I affected by CVE-2026-7831?

Check whether you run UltraVNC Viewer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-7831: UltraVNC Viewer off-by-one stack buffer overflow in RFB handler

CVE-2026-7831 · Severity: high · CVSS 7.6 · Published 2026-07-01

UltraVNC is a remote desktop tool used to control computers over a network. A vulnerability in the viewer component allows a malicious server to crash the software or potentially execute unauthorized code when a user attempts to connect to it. This could lead to a denial of service or a compromise of the user's workstation if they are tricked into connecting to a rogue VNC server.

Vendors: UltraVNC.

Quick answers

Is CVE-2026-7831 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-7831 being exploited in the wild.
How severe is CVE-2026-7831?: High severity, with a CVSS score of 7.6, published 1 July 2026.
Which products and versions are affected?: UltraVNC Viewer through 1.8.2.2.
Is there a fix for CVE-2026-7831?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-7831 attacked?: It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-7831?: Check whether you run UltraVNC Viewer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An off-by-one stack buffer overflow exists in vncviewer/ClientConnection.cpp within the RFB ServerInit message handler. When a server-supplied nameLength is exactly 2024 bytes, the application allocates a 2024-byte stack buffer (_dn[2024]) and calls ReadString(_dn, 2024). The ReadString function writes a NUL terminator at index 2024, which is one byte beyond the buffer's boundary. On systems without stack canaries, this results in a single-byte NUL overwrite of adjacent stack data; on systems with /GS protection, it triggers a stack canary corruption and immediate process termination (DoS). Exploitation requires the user to initiate a connection to a malicious VNC server.

Affected products

uvnc UltraVNC Viewer through 1.8.2.2

Timeline

2026-07-01: disclosed: CVE published to NVD

References

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