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CVE-2026-42221

Nginxui Nginx UI authentication bypass

8.1 HIGHPublic exploitEPSS 1.60%
  1. Published4 May 2026

Description

Nginx UI is a web user interface for the Nginx web server. From version 2.0.0 to before version 2.3.8, an unauthenticated network attacker can claim the initial administrator account on a fresh nginx-ui instance during the first-run setup window. The public /api/install endpoint is reachable without authentication, and the request-encryption flow only protects payload confidentiality in transit; it does not authenticate who is allowed to perform installation. A remote attacker who reaches the service before the legitimate operator can set the admin email, username, and password, causing permanent initial-instance takeover. This issue has been patched in version 2.3.8.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityHigh
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Nginxui Nginx UI≥ 2.0.0 < 2.3.8

Remediation

Fixed in
Nginxui Nginx UI≥ 2.3.8

References

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Frequently asked

Is CVE-2026-42221 being actively exploited?

CVE-2026-42221 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 1.60%.

How severe is CVE-2026-42221?

CVE-2026-42221 has a CVSS 3.1 base score of 8.1, rated high. EPSS estimates a 1.60% probability of exploitation.

Which products are affected by CVE-2026-42221?

Affected products include Nginxui Nginx UI.

How do I fix CVE-2026-42221?

Upgrade affected software to a fixed version, for example Nginxui Nginx UI 2.3.8 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-42221 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.