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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

4 May 2026 20:09:37 UTC

Source modified

5 May 2026 14:14:11 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

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.

Source published

May 4, 2026, 8:09:37 PM (timezone not stated)

Source modified

May 5, 2026, 2:14:11 PM (timezone not stated)

Observed here

7 Nov 2026 09:32:33 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

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.

Source published

4 May 2026 21:16:32 UTC

Source modified

26 Oct 2026 19:10:00 UTC

Observed here

27 Oct 2026 11:12:01 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS 3.1 · [email protected] · Primary · 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

### 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: ```bash 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: ```text [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: ```bash 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: ```text 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 backing database and confirm user ID `1` now belongs to the attacker-controlled username. ### Impact This is an authentication bypass / initial admin claim vulnerability affecting fresh, uninitialized instances that are reachable over the network during the installation window. Any attacker able to reach the service before the legitimate operator can permanently take ownership of the first administrator account and thereby seize control of the application. Because `nginx-ui` is an administrative interface for Nginx and related host-management features, compromise of the initial admin account can lead to unauthorized configuration changes, certificate management abuse, backup manipulation, service disruption, and broader operational takeover of the managed environment. ### Remediation 1. Require a single-use bootstrap secret for installation. Generate the token locally on first start, print it only to the server console or write it to a root-owned local file, and require it on `POST /api/install`. 2. Restrict installation endpoints to loopback by default until setup completes. Remote setup should require an explicit opt-in configuration flag, not be enabled automatically on all interfaces. 3. Make installer claim atomic and explicitly stateful. Persist a dedicated installation state record, consume the bootstrap token exactly once, and refuse concurrent or repeated initialization attempts even within the startup window.

Source published

6 May 2026 16:59:00 UTC

Source modified

25 Jun 2026 23:11:04 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Publisher rating · HIGH

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.

Source published

25 Jun 2026 22:34:31 UTC

Source modified

25 Jun 2026 23:00:54 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.