Brute Force Attack in Buffalo with Basic Auth

A brute force attack against a Buffalo application using HTTP Basic Authentication relies on repeated credential guesses to recover a valid username and password. Because Basic Auth encodes credentials in an easily reversible Base64 string and typically does not enforce strict rate controls, an attacker can systematically submit guessed credentials until one is accepted.

In Buffalo, authentication logic often lives in a before filter (e.g., app/controllers/sessions_controller.go or a custom auth.go filter). If the filter only checks the presence of credentials and does not enforce per-user or per-IP attempt limits, each request returns a clear 401 or 403 response. This deterministic response allows an attacker to reliably distinguish valid from invalid credentials without triggering account lockout.

Basic Auth also lacks built-in salting or key stretching, so captured credentials can be tested offline at high speed. When combined with predictable or reused passwords, this makes brute force feasible even with modest computational resources.

During a black-box scan, middleBrick runs authentication brute force checks as part of its Authentication and Rate Limiting checks. It submits multiple credential pairs to the unprotected endpoint, measures response consistency, and flags endpoints where deterministic 401 responses suggest brute force susceptibility. Findings include severity, guidance to reduce risk, and mapping to frameworks such as OWASP API Top 10 and PCI-DSS.

For example, a vulnerable Buffalo route might look like this, where no rate limiting or attempt tracking is applied:

package controllers

import (
    "github.com/gobuffalo/buffalo"
    "net/http"
)

func Login(c buffalo.Context) error {
    user := c.Param("user")
    pass := c.Param("pass")
    if user == "admin" && pass == "password123" {
        c.Response().Header().Set("Authorization", "Basic "+c.Request().Header.Get("Authorization"))
        return c.Render(200, r.String("OK"))
    }
    return c.Error(401, errors.New("unauthorized"))
}

An attacker can iterate over username/password pairs against this route and observe consistent 401 responses for invalid attempts and a 200 response for valid credentials. Without additional protections such as exponential backoff, token-based challenges, or multi-factor authentication, the attack surface remains wide.

Remediation focuses on reducing the effectiveness of brute force by introducing rate limiting, account lockout, and stronger credential handling within Buffalo handlers.

• Implement per-user rate limiting using middleware to track attempts and introduce delays or temporary blocks.
• Use constant-time comparison to avoid timing leaks when validating credentials.
• Prefer token-based authentication (e.g., JWT) over repeated Basic Auth submissions, and require TLS to protect credentials in transit.
• Return uniform error messages and status codes to avoid revealing whether a username exists.

Example remediation in Buffalo using a simple in-memory attempt tracker and constant-time check:

package controllers

import (
    "crypto/subtle"
    "errors"
    "github.com/gobuffalo/buffalo"
    "net/http"
    "sync"
    "time"
)

var (
    attempts = make(map[string]int)
    mu       sync.Mutex
)

func isLocked(user string) bool {
    mu.Lock()
    defer mu.Unlock()
    return attempts[user] >= 5
}

func recordAttempt(user string) {
    mu.Lock()
    defer mu.Unlock()
    attempts[user]++
    if attempts[user] >= 5 {
        time.AfterFunc(5*time.Minute, func() {
            mu.Lock()
            attempts[user]--
            mu.Unlock()
        })
    }
}

func resetAttempts(user string) {
    mu.Lock()
    attempts[user] = 0
    mu.Unlock()
}

func Login(c buffalo.Context) error {
    if isLocked(c.Param("user")) {
        return c.Error(403, errors.New("too many attempts"))
    }
    user := c.Param("user")
    pass := c.Param("pass")
    // Use a constant-time comparison for the password
    expected := "password123"
    if subtle.ConstantTimeCompare([]byte(pass), []byte(expected)) != 1 {
        recordAttempt(user)
        return c.Error(401, errors.New("unauthorized"))
    }
    resetAttempts(user)
    c.Response().Header().Set("Authorization", "Basic "+c.Request().Header.Get("Authorization"))
    return c.Render(200, r.String("OK"))
}

For production, move attempt tracking to a distributed store (e.g., Redis) and enforce global rate limits at the edge. Combine with HTTPS to protect Basic Auth credentials and consider replacing Basic Auth with session-based or token-based flows where feasible.