Vulnerability Report

CVE-2026-7839

Title: UltraVNC Repeater Hardcoded Default Admin Password

XSS

Proof Of Concept

No public PoC currently indexed for CVE-2026-7839.

CWE Category CWE-798

Published Date Jul 01, 2026

Modified Date Jul 09, 2026

Exploit Status Not Found

Score 9.1 CVSS v3.1

Exploit Probability (EPSS)

0.66%

Vulnerability Summary

CVE-2026-7839: 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.

Impacted Vendors

uvnc 1

Reference Links

https://github.com/ultravnc/UltraVNC https://uvnc.com/

CVSS v3.1

Source Entity 33c584b5-0579-4c06-b2a0-8d8329fcab9c

Severity CRITICAL

9.1

Attack Vector

NETWORK

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

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

Associated Attack Patterns (CAPEC)

Total: Patterns