CVE-2026-7831 Details
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.
A stack buffer overflow vulnerability has been identified in UltraVNC Viewer versions through 1.8.2.2. The issue arises from an off-by-one error in the RFB ServerInit message handler within the vncviewer/ClientConnection.cpp file. When a server advertises a desktop name length of exactly 2024 bytes, the viewer allocates a 2024-byte stack buffer and subsequently calls ReadString to read the name. However, ReadString writes the null terminator one byte past the buffer's end, creating a vulnerability. A malicious VNC server can exploit this by sending a ServerInit message with a name length of 2024.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jul 1, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/ultravnc/UltraVNC | securin | Product |
| https://uvnc.com/ | securin | ProductRelease Notes |
| https://www.securin.io/zero-days/cve-2026-7831-off-by-one-stack-overflow-viewer-namelength-ultravnc | securin |
Weakness Enumeration
Affected Products
| Product | Versions |
|---|---|
| uvnc ultravnc | <= 1.8.2.2 |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 9, 2026 | CVE Modified | securin |
| Jul 2, 2026 | Initial Analysis | [email protected] |
| Jul 1, 2026 | CVE Modified | CISA-ADP |
| Jul 1, 2026 | New CVE Received | securin |