Buffer Overflow Vulnerability in UltraVNC Viewer by UltraVNC
CVE-2026-7831

7.5HIGH

Key Information:

Vendor

Uvnc

Status
Ultravnc
Vendor
CVE Published:
1 July 2026

What is CVE-2026-7831?

UltraVNC Viewer up to version 1.8.2.2 is susceptible to an off-by-one stack buffer overflow caused by improper handling of the RFB ServerInit message. When the server-supplied 'nameLength' equals 2024, the application allocates a 2024-byte stack buffer but incorrectly writes a null terminator outside its bounds, leading to potential corruption of adjacent stack data. This flaw can be exploited by malicious VNC servers advertising a desktop name of length 2024, necessitating user interaction to connect to the compromised server. Depending on whether stack protection mechanisms like canaries are enabled, this vulnerability can either cause a denial of service or allow unintended consequences due to stack data corruption.

Affected Version(s)

UltraVNC 0 <= 1.8.2.2

References

https://uvnc.com/
vendor-advisory
https://github.com/ultravnc/UltraVNC
product

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Arjun Basnet, Securin (arjun.basnet@securin.io)
.