CVE-2026-7831: Off-by-one Error in uvnc UltraVNC
UltraVNC viewer versions through 1.8.2.2 have an off-by-one stack buffer overflow vulnerability in the RFB ServerInit message handler. This occurs when a malicious VNC server advertises a desktop name of length exactly 2024, causing a single-byte overflow past a 2024-byte stack buffer. On builds without stack protection, this can overwrite adjacent stack data; on builds with stack canaries, it causes process termination (denial of service). Exploitation requires user interaction by connecting to a malicious server.
AI Analysis
Technical Summary
CVE-2026-7831 is an off-by-one stack buffer overflow in UltraVNC viewer (up to version 1.8.2.2) within the RFB ServerInit message handler. The vulnerability arises when the server-supplied desktop name length is exactly 2024 bytes. The code allocates a 2024-byte stack buffer and calls ReadString to read the name, which writes a NUL terminator one byte beyond the buffer boundary. This single-byte overflow can overwrite adjacent stack data on release builds without stack canaries or corrupt the stack canary on builds with /GS protection, causing process termination. The attack requires the viewer to connect to a malicious VNC server that sends a crafted ServerInit message.
Potential Impact
Successful exploitation can lead to denial of service due to process termination on builds with stack protection or potential memory corruption on builds without it. The vulnerability has low confidentiality and integrity impact but high availability impact. User interaction is required, as the viewer must connect to a malicious server.
Mitigation Recommendations
No official patch or remediation has been confirmed. Users should avoid connecting UltraVNC viewer versions through 1.8.2.2 to untrusted or malicious VNC servers. Monitor vendor advisories for updates or patches addressing this vulnerability. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.
CVE-2026-7831: Off-by-one Error in uvnc UltraVNC
Description
UltraVNC viewer versions through 1.8.2.2 have an off-by-one stack buffer overflow vulnerability in the RFB ServerInit message handler. This occurs when a malicious VNC server advertises a desktop name of length exactly 2024, causing a single-byte overflow past a 2024-byte stack buffer. On builds without stack protection, this can overwrite adjacent stack data; on builds with stack canaries, it causes process termination (denial of service). Exploitation requires user interaction by connecting to a malicious server.
CVSS v3.1
Score 7.5high
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-7831 is an off-by-one stack buffer overflow in UltraVNC viewer (up to version 1.8.2.2) within the RFB ServerInit message handler. The vulnerability arises when the server-supplied desktop name length is exactly 2024 bytes. The code allocates a 2024-byte stack buffer and calls ReadString to read the name, which writes a NUL terminator one byte beyond the buffer boundary. This single-byte overflow can overwrite adjacent stack data on release builds without stack canaries or corrupt the stack canary on builds with /GS protection, causing process termination. The attack requires the viewer to connect to a malicious VNC server that sends a crafted ServerInit message.
Potential Impact
Successful exploitation can lead to denial of service due to process termination on builds with stack protection or potential memory corruption on builds without it. The vulnerability has low confidentiality and integrity impact but high availability impact. User interaction is required, as the viewer must connect to a malicious server.
Mitigation Recommendations
No official patch or remediation has been confirmed. Users should avoid connecting UltraVNC viewer versions through 1.8.2.2 to untrusted or malicious VNC servers. Monitor vendor advisories for updates or patches addressing this vulnerability. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- securin
- Date Reserved
- 2026-05-05T04:03:22.622Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a44a07a27e9c79719fbd73e
Added to database: 07/01/2026, 05:07:06 UTC
Last enriched: 07/01/2026, 05:21:37 UTC
Last updated: 07/01/2026, 07:03:43 UTC
Views: 5
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