Race Condition in Echo Go with Basic Auth

A race condition in an Echo Go service that uses HTTP Basic Authentication can occur when concurrent requests mutate or read shared authentication state without proper synchronization. Basic Auth typically relies on the client sending an Authorization header on each request; the server validates credentials per request but may rely on shared in-memory data (for example, a cached token-to-user mapping or a rate-limiting structure keyed by username). If validation logic performs a read, then a later write to shared state based on that read, interleaving across goroutines can produce TOCTOU (time-of-check-time-of-use) behavior. An attacker can trigger multiple parallel requests with valid credentials while another goroutine updates a related shared object (such as a per-user request counter or a token revocation list), leading to unexpected outcomes like unauthorized access, privilege confusion, or bypass of intended rate limits.

Consider an endpoint that first checks whether a user is suspended, then proceeds to process a payment. If the suspension flag is stored in a shared map and updated under a mutex while the check is performed without holding the same lock, concurrent valid requests may observe a stale “not suspended” value. In a Basic Auth flow, the username extracted from the Authorization header becomes the key to that shared map; a race between a revocation update and the validation read can allow a suspended user to proceed. This is not a flaw in Basic Auth itself, but in how the application coordinates authentication state across goroutines. The risk is elevated when the implementation mixes authentication checks with business logic mutations on shared variables without consistent locking or isolation, effectively turning a benign credential check into a vector for logic flaws.

middleBrick detects this class of issue by running parallel unauthenticated probes against the authenticated endpoints and analyzing patterns of inconsistent behavior across repeated requests. In the context of the 12 security checks, this manifests as a potential BOLA/IDOR or Business Logic finding when combined with authentication. Because the scanner reviews OpenAPI/Swagger specs and matches runtime findings, it can highlight endpoints where authentication intersects with mutable shared state. Remediation guidance centers on ensuring that any state read as part of authentication decisions is either immutable for the request’s lifetime or protected by synchronization, and that authorization checks are performed close to the point of use with a consistent snapshot of permissions.

To eliminate race conditions when using Basic Auth in Echo Go, synchronize access to shared state and keep authentication checks atomic and side-effect-free for each request. Below are concrete, idiomatic code examples that demonstrate safe patterns.

Example 1: Safe per-request authentication without mutating shared state

import (
	"net/http"
	"strings"

	"github.com/labstack/echo/v4"
)

// BasicAuthValidator validates credentials on each request without mutating shared state.
func BasicAuthValidator(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		auth := c.Request().Header.Get(echo.HeaderAuthorization)
		if auth == "" {
			return echo.ErrUnauthorized
		}
		const prefix = "Basic "
		if !strings.HasPrefix(auth, prefix) {
			return echo.ErrUnauthorized
		}
		payload, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
		if err != nil {
			return echo.ErrUnauthorized
		}
		creds := strings.SplitN(string(payload), ":", 2)
		if len(creds) != 2 || !validCredentials(creds[0], creds[1]) {
			return echo.ErrUnauthorized
		}
		// Attach user info for downstream handlers, no shared mutation.
		c.Set("user", creds[0])
		return next(c)
	}
}

func validCredentials(username, password string) bool {
	// Implement safe lookup, e.g., constant-time compare against a store.
	// Do not modify shared maps or caches here.
	return store[username] == password
}

Example 2: Protecting shared maps with sync.RWMutex to avoid TOCTOU

import (
	"sync"
)

var (
	mu      sync.RWMutex
	suspended = make(map[string]bool) // username -> suspended status
)

// IsUserSuspended safely reads the suspension state.
func IsUserSuspended(username string) bool {
	mu.RLock()
	defer mu.RUnlock()
	return suspended[username]
}

// UpdateSuspension safely writes the suspension state.
func UpdateSuspension(username string, suspendedStatus bool) {
	mu.Lock()
	defer mu.Unlock()
	suspended[username] = suspendedStatus
}

// Usage in a handler: check suspension atomically before proceeding.
func PaymentHandler(c echo.Context) error {
	user := c.Get("user").(string)
	if IsUserSuspended(user) {
		return echo.ErrForbidden
	}
	// Proceed with payment logic.
	return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
}

Key principles: keep the validation function side-effect-free, avoid mutating shared maps during read-only authorization steps, and guard any shared structure with appropriate mutexes or use sync/atomic patterns. These changes prevent interleaved updates from corrupting the state observed during authentication checks, thereby removing the race condition while preserving Basic Auth’s simplicity.