FileBrowser: Missing Rate Limiting on Authentication Endpoint Enables Brute Force Attacks

Summary

The /api/auth/login endpoint does not implement rate limiting, account lockout, or progressive backoff for repeated authentication failures. As a result, an attacker can perform unlimited login attempts against the endpoint. When combined with the username enumeration timing vulnerability, valid accounts can be identified and then brute-forced without restriction. The risk is further increased by a weak default password policy that only enforces a minimum length of five characters.

Details

The authentication endpoint /api/auth/login does not enforce any form of rate limiting, account lockout, or progressive backoff for repeated failed login attempts. Testing confirmed that the endpoint accepts an unlimited number of authentication attempts from the same client without delay or restriction.

This allows attackers to repeatedly attempt password guesses against valid usernames.

Secure authentication systems typically enforce request throttling, temporary account lockout, or progressive delays after repeated failed login attempts to mitigate brute-force attacks.

$ python rate-limit-probe.py
[*] Probing http://localhost/api/auth/login for rate limiting, lockout, and backoff behavior...
    Attempt  10: status=401, latency=0.0411s
    Attempt  20: status=401, latency=0.0411s
    Attempt  30: status=401, latency=0.0402s
    Attempt  40: status=401, latency=0.0420s
    Attempt  50: status=401, latency=0.0403s
    Attempt  60: status=401, latency=0.0423s
    Attempt  70: status=401, latency=0.0474s
    Attempt  80: status=401, latency=0.0417s
    Attempt  90: status=401, latency=0.0407s
    Attempt 100: status=401, latency=0.0407s

--- CONCRETE EVIDENCE ---
Attempts completed:        100
Total runtime:             4.17s
Average request rate:      23.98 req/sec
Unique status codes:       [401]
Average time (first 5):    0.0447s
Average time (last 5):     0.0408s
Latency delta:             -0.0038s
[RESULT] No HTTP 429 responses observed.
[RESULT] No progressive backoff detected: response timing remained effectively constant.

Additional Context

Password validation is implemented in backend/database/storage/bolt/user.go via checkPassword(), which only verifies that the supplied password length is greater than or equal to settings.Config.Auth.Methods.PasswordAuth.MinLength. In backend/common/settings/auth.go, the PasswordAuthConfig documents the default value of MinLength as 5. No additional complexity requirements, such as uppercase, lowercase, numeric, or special character checks, were identified in this code path.

PoC

The script below demonstrates the lack of rate limiting by performing a high volume automated authentication test. The script sends sequential login requests and monitors for HTTP 429 (Too Many Requests) status codes.