How severe is CVE-2026-7839?

CVE-2026-7839 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-7839 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-7839?

CVE-2026-7839 affects Uvnc Ultravnc. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-7839?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2026-7839 published?

CVE-2026-7839 was published on 2026-07-01 and last updated on 2026-07-02.

CVE-2026-7839

CVE-2026-7839 is a critical-severity vulnerability in Uvnc Ultravnc with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-798.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 0% (25th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-798
Affected product: Uvnc Ultravnc
Published: 2026-07-01
Last modified: 2026-07-02

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-7839?: CVE-2026-7839 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-7839 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-7839?: CVE-2026-7839 affects Uvnc Ultravnc. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-7839?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2026-7839 published?: CVE-2026-7839 was published on 2026-07-01 and last updated on 2026-07-02.

References

Affected products (1)

cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*

More vulnerabilities in Uvnc Ultravnc

CVE-2019-8280 — Critical (CVSS 9.8): UltraVNC revision 1203 has out-of-bounds access vulnerability in VNC client inside RAW decoder, which can potentially…
CVE-2019-8275 — Critical (CVSS 9.8): UltraVNC revision 1211 has multiple improper null termination vulnerabilities in VNC server code, which result in…
CVE-2019-8274 — Critical (CVSS 9.8): UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer offer handler,…
CVE-2019-8273 — Critical (CVSS 9.8): UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer request…
CVE-2019-8272 — Critical (CVSS 9.8): UltraVNC revision 1211 has multiple off-by-one vulnerabilities in VNC server code, which can potentially result in code…
CVE-2019-8271 — Critical (CVSS 9.8): UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer handler, which…

All CVEs affecting Uvnc Ultravnc →

Other CWE-798 (Use of Hard-coded Credentials) vulnerabilities

CVE-2026-13768 — Critical (CVSS 10.0): Gardyn devices expose a privileged iothubowner key. Access to this key will allow a malicious user to invoke an IoTHub…
CVE-2026-45631 — Critical (CVSS 10.0): Dokploy is a free, self-hostable Platform as a Service (PaaS). From 0.27.0 to before 0.29.3, a hardcoded…
CVE-2026-22769 — Critical (CVSS 10.0): Dell RecoverPoint for Virtual Machines, versions prior to 6.0.3.1 HF1, contain a hardcoded credential vulnerability.…
CVE-2025-42890 — Critical (CVSS 10.0): SQL Anywhere Monitor (Non-GUI) baked credentials into the code,exposing the resources or functionality to unintended…
CVE-2025-7503 — Critical (CVSS 10.0): An OEM IP camera manufactured by Shenzhen Liandian Communication Technology LTD exposes a Telnet service (port 23) with…
CVE-2025-20309 — Critical (CVSS 10.0): A vulnerability in Cisco Unified Communications Manager (Unified CM) and Cisco Unified Communications Manager Session…

Browse all CWE-798 (Use of Hard-coded Credentials) vulnerabilities →