How severe is CVE-2026-34403?

CVE-2026-34403 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-34403 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-34403?

CVE-2026-34403 affects Nginxui Nginx Ui. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-34403?

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

Does CVE-2026-34403 have an EU (EUVD) identifier?

Yes. CVE-2026-34403 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23972.

When was CVE-2026-34403 published?

CVE-2026-34403 was published on 2026-04-20 and last updated on 2026-06-17.

CVE-2026-34403

CVE-2026-34403 is a high-severity vulnerability in Nginxui Nginx Ui with a CVSS 3.x base score of 8.1. 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-1385.

Key facts

Severity: High (CVSS 3.x base score 8.1)
CVSS v4: 5.5
EPSS exploit prediction: 0% (7th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-23972
Weakness: CWE-1385
Affected product: Nginxui Nginx Ui
Published: 2026-04-20
Last modified: 2026-06-17

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.

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.
How severe is CVE-2026-34403?: CVE-2026-34403 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-34403 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-34403?: CVE-2026-34403 affects Nginxui Nginx Ui. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-34403?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-34403 have an EU (EUVD) identifier?: Yes. CVE-2026-34403 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23972.
When was CVE-2026-34403 published?: CVE-2026-34403 was published on 2026-04-20 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:nginxui:nginx_ui:*:*:*:*:*:*:*:*

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