CVE-2026-7829
HighCVSS 7.2Exploitation Probability (EPSS)
Low risk39th percentile — higher than 39% of all known CVEs
Summary
A post-authentication out-of-bounds write vulnerability in UltraVNC repeater through version 1.8.2.2 exists in the allow/deny rule parser. The code writes a NUL terminator without clamping the length to the destination buffer size, potentially corrupting stack data.
Risk Assessment
An attacker with admin credentials (including via CVE-2026-7839 default password) can trigger this to achieve code execution on the repeater host, leading to full system compromise.
Recommendation
Update UltraVNC repeater to a version newer than 1.8.2.2 immediately and change default admin passwords to prevent unauthorized access.
Original NVD description (English source)
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.