Public proof of conceptFix available

CVE-2026-42221

Q: Is CVE-2026-42221 actively exploited?

A proof-of-concept exploit exists for CVE-2026-42221, but active exploitation has not been confirmed at this time.

Q: What is the CVSS score for CVE-2026-42221?

CVE-2026-42221 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

A public proof of concept exists; no exploitation attested.

Published2026-05-04
Fixed in2.3.8
WeaknessCWE-306

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2026-05-0421:16CVE publishedNVD
2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-42221?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-42221?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Nginxui nginx ui

Branch	Affected	Fixed in	Source
2.x	≥ 2.0.0, < 2.3.8	2.3.8	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Nginxui nginx ui to 2.3.8

Advisories and patches

github.comRelease Notes
github.comMitigation · Vendor Advisory

Detection

read 2026-10-23 19:25 UTC

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: 1 repository, unverifiedfuchiuebusi-lab/nginx-ui-CVE-2026-42221-CVE-2026-42238-

Sources

CISA-ADPSSVC decisionpoc2026-05-05
OpenCVESSVC decisionpoc—
CNACVSS 3.18.1read 2026-10-23
NVDCVSS 3.19.8read 2026-10-23
CNAweakness (CWE)CWE-306read 2026-10-23
FIRST EPSSEPSS score1.6 %2026-10-22
PoC-in-GitHubproof of concept1read 2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2026-05-04
Last Modified: 2026-06-17
NVD status: Analyzed

Frequently asked questions

What is CVE-2026-42221?

Is CVE-2026-42221 actively exploited?

A proof-of-concept exploit exists for CVE-2026-42221, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-42221?

CVE-2026-42221 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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