CVE-2026-7839 CRITICAL

CVE-2026-7839: UltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin access

Vendor Uvnc
Product UltraVNC
Weakness CWE-798 · Hardcoded credentials
Published July 1, 2026
Last update July 1, 2026

CVSS base score

9.1/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality High
Integrity High

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

What the vulnerability does

01Description

UltraVNC repeater through 1.8.2.2 initializes the HTTP administration server with a hardcoded default password. In repeater/webgui/settings.c:197, when settings2.txt is absent on first run the repeater writes the literal string "adminadmi2" as the admin password via strcpy_s(saved_password, 64, "adminadmi2"). The HTTP Basic-auth handler wi_decode_auth() checks this password without rate-limiting or lockout. Any remote attacker who can reach the repeater HTTP port (default TCP 80) can authenticate as administrator using the well-known default credential on a fresh or unmodified installation, gaining full control of the repeater configuration including allow/deny rules and session visibility.

Key dates

02Disclosure timeline

July 1, 2026 CVE published