CVE-2026-7839: critical vulnerability in uvnc UltraVNC
UltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin access
Published · Updated
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.1epss 0.7%
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Affected products
uvnc · UltraVNCRelated CVEs — uvnc UltraVNC
In the same product, most dangerous first.
CVE-2026-7840CRITICALUltraVNC repeater HTTP server global buffer overflow via long URI (pre-auth RCE)EPSS 2.6%CVE-2026-7838HIGHUltraVNC viewer heap buffer overflow via integer overflow in RFB connection-failure reason lengthEPSS 1.9%CVE-2026-7828MEDIUMUltraVNC repeater integer overflow in win_log malloc leading to heap overflowEPSS 1.4%CVE-2026-7829HIGHUltraVNC repeater authenticated out-of-bounds write in rule parser via oversized tokenEPSS 0.9%CVE-2026-7831HIGHUltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsingEPSS 0.7%CVE-2026-44042LOWUltraVNC repeater wi_uudecode off-by-one in base64 decode boundary checkEPSS 0.5%