CVE-2026-7831
UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.74%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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 3.1
- 7.6 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
- EPSS
- 0.74% probability · 53th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-193, CWE-787
- Affected
- uvnc/ultravnc
- Source
- 33c584b5-0579-4c06-b2a0-8d8329fcab9c
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.