CVE-2026-42221: Nginx UI is a web user interface for the Nginx web server

Q: How do I fix CVE-2026-42221?

nginx ui: upgrade to 2.3.8. Exact commands for each OS are on this page.

Q: Is CVE-2026-42221 being exploited?

CVE-2026-42221 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-42221 affect?

CVE-2026-42221 affects nginx ui. Severity is high (CVSS 8.1). 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 w

Q: How urgent is CVE-2026-42221?

Priority 61/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

This week

HIGH 8.1REMOTEWATCHLISTUPGRADE

CVE-2026-42221 is a high-severity flaw (CVSS 8.1) affecting nginx ui. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 29%)
CISA exploited list	No
Weakness	CWE-306
Published	2026-05-04
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: nginxui

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-04 21:16 UTCPublished CVE record published
2026-10-26 19:10 UTCUpdated Record last modified

nginxui nginx ui UPGRADE

Affected: >= 2.0.0 and < 2.3.8

Fixed in: 2.3.8

Safe to downgrade to: a release before 2.0.0

1. Check installed version

apt-cache policy nginx-ui || rpm -q nginx-ui || nginx-ui --version

2. UPGRADE to 2.3.8 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nginx-ui

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nginx-ui

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.0.0 (Debian / Ubuntu)

apt-cache madison nginx-ui sudo apt install nginx-ui=<VERSION_BEFORE_2.0.0> sudo apt-mark hold nginx-ui

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nginx-ui sudo dnf downgrade nginx-ui-<VERSION_BEFORE_2.0.0> sudo dnf versionlock add nginx-ui

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Go · github.com/0xJacky/Nginx-UI · FIXED · 2.3.8 · vulnerable: >= 2.0.0, <= 2.3.5 · source

go get github.com/0xJacky/Nginx-UI@v2.3.8 go list -m github.com/0xJacky/Nginx-UI

Fedora 46 · ddnet · FIXED · 20.2-1.fc46 · FEDORA-2026-6991b4ab14 · source

sudo dnf upgrade --advisory=FEDORA-2026-6991b4ab14

Fedora ELN · libplacebo · FIXED · 7.360.1-5.eln159 · FEDORA-2026-92226f221e · source

sudo dnf upgrade --advisory=FEDORA-2026-92226f221e

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: fuchiuebusi-lab/nginx-ui-CVE-2026-42221-CVE-2026-42238- (0 stars)
Write-up: github.com/0xJacky/nginx-ui/security/advisories/GHSA-h27v-ph7w-m9fp
Nuclei scan template: Nginx UI <= 2.3.7 - Unauthenticated Installer Exposure

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42221?

nginx ui: upgrade to 2.3.8. Exact commands for each OS are on this page.

Is CVE-2026-42221 being exploited?

CVE-2026-42221 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42221 affect?

CVE-2026-42221 affects nginx ui. Severity is high (CVSS 8.1). 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 w

How urgent is CVE-2026-42221?

Priority 61/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

nginx vulnerabilities

Related CVEs

CVE-2026-34403 HIGH 8.1 UPGRADE Nginx UI is a web user interface for the Nginx web server
CVE-2026-42222 HIGH 8.1 DOWNGRADE Nginx UI is a web user interface for the Nginx web server
CVE-2026-42220 MEDIUM 6.5 UPGRADE Nginx UI is a web user interface for the Nginx web server
CVE-2026-42223 MEDIUM 6.5 UPGRADE Nginx UI is a web user interface for the Nginx web server
CVE-2026-44015 HIGH 8.5 UPGRADE Nginx UI is a web user interface for the Nginx web server

References

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