What’s Vulnerable › Vulnerabilities

CVE-2026-7829: UltraVNC repeater authenticated out-of-bounds write in rule parser via oversized token

• Severity: high (CVSS 7.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-01 · updated 2026-10-25
• Weakness: CWE-787

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.

Affected products

• Kaspersky Lab UltraVNC: through 1.8.2.2

References

• https://github.com/ultravnc/UltraVNC
• https://uvnc.com/
• https://www.securin.io/zero-days/cve-2026-7829-post-auth-oob-nul-write-repeater-rule-parser-ultravnc

Get alerted when CVE-2026-7829 or the next vulnerability affects your stack