CVE-2026-7829: uvnc ultravnc Out-of-bounds Write

Vulnerability summary

CVE-2026-7829 is a high (CVSS 7.2) Out-of-bounds Write vulnerability in uvnc ultravnc. EPSS estimates a 0.85% chance of exploitation in the next 30 days, higher than 57.5% of scored vulnerabilities.

Timeline

1. 01-07-2026
   PublishedVulnerability first disclosed.
2. 09-07-2026
   Last modifiedVulnerability information updated.

Description

UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the allow/deny rule parser. In repeater/webgui/settings.c:225-272, after strncpy_s copies a rule token into temp1[rule1] (25-byte destination) or temp2/temp3 (16-byte destination), the code unconditionally writes a NUL terminator at temp1[rule1][len] = 0 without clamping len to the destination size. When an authenticated administrator saves a rule with a token length equal to or greater than the destination size, the NUL byte is written one or more bytes past the end of the stack-allocated array, corrupting adjacent stack data. An attacker who has obtained admin credentials (including via CVE-2026-7839 default password) can trigger this to gain code execution on the repeater host.

• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.