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CVE-2026-42221

nginx-ui: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

8.1 HighPublic exploitFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

1.34%Up 1.3 points since May 5, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.1

nginx-ui: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

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.

Record
CVE-2026-42221
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-306
Updated
2026-11-02
EUVDEUVD-2026-27135 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 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.

Record
EUVD-2026-27135
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-h27v-ph7w-m9fp 8.1

Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

Summary

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.

Details

The vulnerable route is exposed publicly through the main API router. router/routers.go:61-70 mounts system.InitPublicRouter(root) under /api, and api/system/router.go:16-19 registers both GET /api/install and POST /api/install without AuthRequired().

The install handler only checks whether the instance is already installed and whether more than ten minutes have elapsed since startup. api/system/install.go:26-33 treats the instance as uninstalled when JwtSecret is empty and SkipInstallation is false. api/system/install.go:56-69 rejects requests only if installation has already happened or the ten-minute window has expired.

If those checks pass, the unauthenticated caller controls the initialization flow. api/system/install.go:77-81 generates and saves the JWT secret, node secret, and certificate email from attacker-controlled input, and api/system/install.go:93-97 overwrites user ID 1 with the attacker-chosen username and password hash. internal/kernel/init_user.go:15-22 guarantees that privileged user ID 1 exists ahead of time, so there is always an account to claim.

The public-key bootstrap does not add authentication. api/crypto/router.go:5-9 exposes POST /api/crypto/public_key publicly, api/crypto/crypto.go:12-32 returns a server public key to any caller, internal/crypto/crypto.go:44-61 stores a shared keypair in cache, and internal/middleware/encrypted_params.go:25-50 only decrypts encrypted_params before passing the request to the install handler. No request ID, local-only restriction, bootstrap secret, or prior trust check is enforced.

This was verified locally in an isolated lab instance. A fresh instance returned {"lock":false,"timeout":false}, an unauthenticated POST /api/install returned {"message":"ok"}, the instance then flipped to {"lock":true,"timeout":false}, and the on-disk SQLite database showed user ID 1 renamed to the attacker-controlled username with a non-empty password hash.

PoC

The quickest local verification path is the helper script created during validation:

ATTACKER_EMAIL='[email protected]' ATTACKER_USER='attacker' ATTACKER_PASS='Password12345' \
'/Users/r1zzg0d/Documents/CVE hunting/targets/nginx-ui/output/verify/verify_fresh_install_takeover.sh'

Expected proof points:

[1/6] Fresh-instance status:
{
  "lock": false,
  "timeout": false
}

[3/6] Claiming the initial administrator account...
{
  "message": "ok"
}

[4/6] Verifying install is now locked...
{
  "lock": true,
  "timeout": false
}

[5/6] Verifying the on-disk admin record was overwritten...
{
  "id": 1,
  "name": "attacker",
  "password_len": 60
}

To confirm the final state manually:

sqlite3 '/Users/r1zzg0d/Documents/CVE hunting/targets/nginx-ui/tmp/poc-install-takeover/database.db' \
'select id,name,length(password) from users where id=1;'

Expected output:

1|attacker|60

Manual HTTP reproduction is also straightforward:

  1. Request GET /api/install and confirm lock=false and timeout=false.
  2. Request POST /api/crypto/public_key to obtain the public RSA key.
  3. Encrypt {"email":"[email protected]","username":"attacker","password":"Password12345"} with that public key and base64-encode the ciphertext.
  4. Submit the ciphertext to POST /api/install as {"encrypted_params":"..."}.
  5. Re-request GET /api/install and observe that lock=true.
  6. Inspect the…
Record
GHSA-h27v-ph7w-m9fp
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-306
Updated
2026-11-02
NVD 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 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.

Record
CVE-2026-42221
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-306
Updated
2026-11-02
OSV 8.1

nginx-ui: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

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.

Record
CVE-2026-42221
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-306
Updated
2026-11-02
OSVGHSA-h27v-ph7w-m9fp 8.1

Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim

Summary

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.

Details

The vulnerable route is exposed publicly through the main API router. router/routers.go:61-70 mounts system.InitPublicRouter(root) under /api, and api/system/router.go:16-19 registers both GET /api/install and POST /api/install without AuthRequired().

The install handler only checks whether the instance is already installed and whether more than ten minutes have elapsed since startup. api/system/install.go:26-33 treats the instance as uninstalled when JwtSecret is empty and SkipInstallation is false. api/system/install.go:56-69 rejects requests only if installation has already happened or the ten-minute window has expired.

If those checks pass, the unauthenticated caller controls the initialization flow. api/system/install.go:77-81 generates and saves the JWT secret, node secret, and certificate email from attacker-controlled input, and api/system/install.go:93-97 overwrites user ID 1 with the attacker-chosen username and password hash. internal/kernel/init_user.go:15-22 guarantees that privileged user ID 1 exists ahead of time, so there is always an account to claim.

The public-key bootstrap does not add authentication. api/crypto/router.go:5-9 exposes POST /api/crypto/public_key publicly, api/crypto/crypto.go:12-32 returns a server public key to any caller, internal/crypto/crypto.go:44-61 stores a shared keypair in cache, and internal/middleware/encrypted_params.go:25-50 only decrypts encrypted_params before passing the request to the install handler. No request ID, local-only restriction, bootstrap secret, or prior trust check is enforced.

This was verified locally in an isolated lab instance. A fresh instance returned {"lock":false,"timeout":false}, an unauthenticated POST /api/install returned {"message":"ok"}, the instance then flipped to {"lock":true,"timeout":false}, and the on-disk SQLite database showed user ID 1 renamed to the attacker-controlled username with a non-empty password hash.

PoC

The quickest local verification path is the helper script created during validation:

ATTACKER_EMAIL='[email protected]' ATTACKER_USER='attacker' ATTACKER_PASS='Password12345' \
'/Users/r1zzg0d/Documents/CVE hunting/targets/nginx-ui/output/verify/verify_fresh_install_takeover.sh'

Expected proof points:

[1/6] Fresh-instance status:
{
  "lock": false,
  "timeout": false
}

[3/6] Claiming the initial administrator account...
{
  "message": "ok"
}

[4/6] Verifying install is now locked...
{
  "lock": true,
  "timeout": false
}

[5/6] Verifying the on-disk admin record was overwritten...
{
  "id": 1,
  "name": "attacker",
  "password_len": 60
}

To confirm the final state manually:

sqlite3 '/Users/r1zzg0d/Documents/CVE hunting/targets/nginx-ui/tmp/poc-install-takeover/database.db' \
'select id,name,length(password) from users where id=1;'

Expected output:

1|attacker|60

Manual HTTP reproduction is also straightforward:

  1. Request GET /api/install and confirm lock=false and timeout=false.
  2. Request POST /api/crypto/public_key to obtain the public RSA key.
  3. Encrypt {"email":"[email protected]","username":"attacker","password":"Password12345"} with that public key and base64-encode the ciphertext.
  4. Submit the ciphertext to POST /api/install as {"encrypted_params":"..."}.
  5. Re-request GET /api/install and observe that lock=true.
  6. Inspect the…
Record
GHSA-h27v-ph7w-m9fp
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-306
Updated
2026-11-02
OSVGO-2026-5412 No score

Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim in github.com/0xJacky/Nginx-UI

Nginx-UI: Unauthenticated First-Run Installer Allows Remote Initial Admin Claim in github.com/0xJacky/Nginx-UI.

NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions.

(If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.)

The additional affected modules and versions are: github.com/0xJacky/Nginx-UI from v2.0.0 before v2.3.8.

Record
GO-2026-5412
Updated
2026-11-02
OSVopenSUSE-SU-2026:21483-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

  • Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

  • GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
  • GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
  • GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
  • GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
  • GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
  • GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
  • GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
  • GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
  • GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
  • GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
  • GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
  • GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
  • GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
  • GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
  • GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
  • GO-2026-5933 GHSA-3g4q-2f67-2gvh
  • GO-2026-5934 GHSA-59qp-cfj3-rp64
  • GO-2026-5935 GHSA-7856-g3gv-9wq8
  • GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
  • GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
  • GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
  • GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
  • GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
  • GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
  • GO-2026-5942 CVE-2026-46600
  • GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
  • GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
  • GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
  • GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
  • GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
  • GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
  • GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
  • GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
  • GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
  • GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
  • GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
  • GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
  • GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
  • GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
  • GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
  • GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
  • GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
  • GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
  • GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
  • GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
  • GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
  • GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
  • GO-2026-5969 GHSA-g936-7jqj-mwv8
  • GO-2026-5970 CVE-2026-56852
  • GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
  • GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
  • GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
  • GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
  • GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
  • GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
  • GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
  • GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
  • GO-2026-5981 GHSA-mqxv-9rm6-w8qc
  • GO-2026-5982 GHSA-pqg7-v6wh-3pfp
  • GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
  • GO-2026-5985 GHSA-7rx3-5wx3-5v76
  • GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
  • GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
  • GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
  • GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
  • GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
  • GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
  • GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
  • GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
  • GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
  • GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
  • GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
  • GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
  • GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
  • GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
  • GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
  • GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…
Record
openSUSE-SU-2026:21483-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
github.com/0xJacky/Nginx-UI
Go
 2.0.0 to 2.3.5
2.3.8
github.com/0xJacky/Nginx-UI
Go
 2.0.0 up to 2.3.8
2.3.8
github.com/0xJacky/Nginx-UI
Go
 All versions None known
govulncheck-vulndb
openSUSE:Leap 16.0
From an advisory covering 1734 CVEs
 before 0.0.20260723T184607-160000.1.1
0.0.20260723T184607-160000.1.1

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
SourceLinkDate
PoC in GitHubfuchiuebusi-lab/nginx-ui-CVE-2026-42221-CVE-2026-42238-2026-06-23
NucleiNginx UI <= 2.3.7 - Unauthenticated Installer Exposure

History

History
RecordedChangedSources
affected, exploits, facts
first indexedCVE List, EUVD, GitHub Advisories, Nuclei, NVD, OSV, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-42221 is a high vulnerability (CVSS 8.1) in 0xjacky Nginx-ui, published May 4, 2026. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 1.34%, the 71st percentile. Fixed in github.com/0xJacky/Nginx-UI 2.3.8.

References

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