CVE-2026-7839 UltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin access
Remote attackers can gain full administrative control of UltraVNC repeater by using a hardcoded default password on fresh installations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-7839?
CVE-2026-7839 is a critical vulnerability in uvnc UltraVNC, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-798
Which versions are affected by CVE-2026-7839?
It affects 1 product.
Products include Uvnc Ultravnc.
How do I fix CVE-2026-7839?
No fix has been published for CVE-2026-7839 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-7839 being exploited?
There is no known exploitation of CVE-2026-7839 in the wild and no public exploit code.
Other vulnerabilities in uvnc UltraVNC
Sources
Also known as GHSA-h7cc-6wq3-9h7x.