CVE-2026-34403: nginx ui — Exploit & Fix

Description

Nginx UI is a web user interface for the Nginx web server. Prior to version 2.3.5, all WebSocket endpoints in nginx-ui use a gorilla/websocket Upgrader with CheckOrigin unconditionally returning true, allowing Cross-Site WebSocket Hijacking (CSWSH). Combined with the fact that authentication tokens are stored in browser cookies (set via JavaScript without HttpOnly or explicit SameSite attributes), a malicious webpage can establish authenticated WebSocket connections to the nginx-ui instance when a logged-in administrator visits the attacker-controlled page. Version 2.3.5 patches the issue.

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CVSS v3.1 Score

8.1

HIGH

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

EPSS — Exploit Prediction

0.0003

Probability of exploitation

0.08%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-1385 CWE-1385

Affected Products

Vendor	Product	Versions
nginxui	nginx_ui	< 2.3.5

References

Advisories & Patches

https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-78mf-482w-62qj

Exploits

https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-78mf-482w-62qj

Other References

https://github.com/0xJacky/nginx-ui/releases/tag/v2.3.5

Frequently Asked Questions

What is CVE-2026-34403? +

Nginx UI is a web user interface for the Nginx web server. Prior to version 2.3.5, all WebSocket endpoints in nginx-ui use a gorilla/websocket Upgrader with CheckOrigin unconditionally returning true, allowing Cross-Site WebSocket Hijacking (CSWSH). Combined with the fact that authentication tokens are stored in browser cookies (set via JavaScript without HttpOnly or explicit SameSite attributes), a malicious webpage can establish authenticated WebSocket connections to the nginx-ui instance when a logged-in administrator visits the attacker-controlled page. Version 2.3.5 patches the issue. It has a CVSS v3.1 base score of 8.1 (HIGH).

How severe is CVE-2026-34403? +

CVE-2026-34403 has a CVSS v3.1 score of 8.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0003, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-34403? +

CVE-2026-34403 affects products from nginxui, specifically: nginx_ui. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-34403? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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