Use After Free in Echo Go with Basic Auth

A Use After Free (UAF) class of bug occurs when memory is deallocated but pointers to it remain in use, leading to unpredictable behavior or potential code execution. In Echo Go, combining Basic Authentication with UAF typically arises when request-scoped objects (e.g., parsed credentials or context-bound buffers) are freed while an asynchronous handler or middleware still references them.

Consider a handler that parses Basic Auth credentials, stores them in a request context value, and then frees the underlying byte buffer before the request completes. If a deferred cleanup function or a background goroutine references the freed buffer while handling the request, the reference becomes dangling. In Go, this is less common due to garbage collection, but UAF-like issues can still manifest via unsafe patterns such as unsafe.Pointer manipulation, Cgo interop, or retention of slices over buffers that are later reused or released.

When Basic Auth credentials are extracted and stored in a mutable buffer that is subsequently freed or reused, an attacker may trigger the condition by sending rapid, concurrent requests or by leveraging timing differences in goroutine scheduling. The scanner’s checks include input validation and unsafe consumption checks that can surface suspicious patterns where credential material is handled in ways that risk memory safety, even in a managed runtime, particularly when interoperating with lower-level code.

An example vulnerability chain:

1. Client sends a request with an Authorization: Basic base64(credentials) header.
2. Middleware decodes credentials into a byte slice and stores a pointer in a request-local context to avoid re-parsing.
3. Handler completes, and an explicit or implicit cleanup routine frees or reuses the underlying memory backing the slice (e.g., returning it to a sync.Pool or overwriting it).
4. A deferred function or a concurrently running goroutine still reads from the stored pointer, resulting in a Use After Free condition.

Because middleBrick tests input validation and unsafe consumption, it flags scenarios where credential data is retained beyond its intended lifetime or where outputs from authentication are used after presumed cleanup, even if the exact memory layout is abstracted by Go.

To prevent Use After Free and related memory-safety issues when using Basic Auth in Echo Go, ensure credentials are copied into immutable, request-scoped values and avoid retaining pointers to buffers that may be freed or reused. Prefer standard library patterns and avoid unsafe manipulation of memory.

Secure Basic Auth parsing and usage

Parse credentials early, copy the values, and store only safe, high-level types (e.g., strings) in request context. Do not retain references to buffers that may be reused.

// Good: parse and copy credentials, store as strings in context
func basicAuthMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        auth := c.Request().Header.Get("Authorization")
        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
        }
        // Copy credentials into immutable values
        creds := string(payload) // safe: Go strings are immutable
        // Store a copy in context, not a pointer to transient buffers
        c.Set("auth_creds", creds)
        return next(c)
    }
}

Avoid unsafe patterns

Do not use unsafe.Pointer or Cgo to pass credential buffers between layers unless you have strict control over lifetimes and synchronization. If interoperability requires it, ensure copies are made and the original buffers are not freed while in use.

// Avoid: do not retain pointers to buffers that may be freed
// This is illustrative; Go typically manages memory safely.
func unsafeExample(ptr *byte) { /* do not use credential pointer beyond request scope */ }

Middleware and handler discipline

Ensure middleware does not free or reuse buffers that handlers may read after middleware returns. Use value copies and avoid pooling buffers that contain sensitive credential material unless the pool is designed for safe, cleared reuse.

// Good: handler uses copied values, no dangling references
func handleRequest(c echo.Context) error {
    creds, ok := c.Get("auth_creds").(string)
    if !ok || creds == "" {
        return echo.ErrUnauthorized
    }
    // Use creds safely; no references to freed memory
    return c.String(http.StatusOK, "authenticated")
}

Leverage middleBrick findings

Use the input validation and unsafe consumption checks from middleBrick to detect risky patterns where credential material might be handled in a way that risks Use After Free. The scanner’s LLM/AI Security checks can also help identify logic flows where authentication state is improperly managed across asynchronous boundaries.