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Vulnerability details

CVE-2026-7831

uvnc UltraVNC

UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing

CVSS 3.1
7.5High

Official 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.

CVSS scores

ScoreVersionSourceVector
7.5High 3.1 CVEProject cvelistV5 (CNA) (securin) CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

Affected products

VendorProductVersionsSource
uvnc UltraVNC v ≤ 1.8.2.2 CVEProject cvelistV5 (CNA)

References and advisories

3
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Details

Published
2026-07-01
Last updated
2026-07-09
State
Published
Assigner (CNA)
securin

Exploit prediction (EPSS)

0.73%
Probability of exploitation in 30 days
54.7%
Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable
No
Exploitation
None
Technical impact
Partial

Weaknesses (CWE)

  • CWE-193
    Off-by-one Error
  • CWE-787
    Out-of-bounds Write