# CVE-2026-7831

## Summary

- **CVE ID:** CVE-2026-7831
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H)
- **CWE:** CWE-193, CWE-787
- **Published:** Jul 1, 2026
- **Last Modified:** Jul 9, 2026

## Description

UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required.

## Affected Products

- uvnc — UltraVNC (0)

## References

- [CNA](https://uvnc.com/)
- [CNA](https://github.com/ultravnc/UltraVNC)
- [CNA](https://www.securin.io/zero-days/cve-2026-7831-off-by-one-stack-overflow-viewer-namelength-ultravnc)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.74%
- **EPSS Percentile:** 52.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._