Use After Free in Echo Go

Use After Free (UAF) vulnerabilities in Echo Go occur when a pointer to freed memory is accessed after the memory has been deallocated. In Echo Go applications, this typically manifests through Echo's context handling, middleware chains, and HTTP request lifecycle management.

The most common Echo Go UAF pattern involves middleware that captures references to request-scoped objects, then attempts to use those objects after the request has completed and memory has been reclaimed by Go's garbage collector. Consider this problematic pattern:

func vulnerableMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    var requestData *RequestData
    
    return func(c echo.Context) error {
        requestData = &RequestData{ID: c.Request().Context().Value("request_id")}
        
        // Middleware chain continues
        err := next(c)
        
        // Request completes, but requestData still referenced
        go func() {
            // UAF: requestData may be freed, but we access it
            log.Printf("Request %v completed", requestData.ID)
        }()
        
        return err
    }
}

The goroutine captures requestData which points to stack-allocated memory that becomes invalid after the HTTP handler returns. When the goroutine executes, it accesses freed memory.

Another Echo Go-specific UAF scenario involves Echo's Context object lifecycle. Echo's context pool reuses echo.Context instances across requests for performance. If middleware stores a pointer to c and uses it after the request completes, it may access memory that has been reallocated for a new request:

func contextPoolUAF(next echo.HandlerFunc) echo.HandlerFunc {
    var savedContext *echo.Context
    
    return func(c echo.Context) error {
        savedContext = &c // Store pointer to context
        
        // Simulate async operation
        time.AfterFunc(2*time.Second, func() {
            // UAF: savedContext may point to memory now used by another request
            fmt.Println((*savedContext).Request().URL)
        })
        
        return next(c)
    }
}

This creates a classic use-after-free where the context pointer references memory that Echo has reassigned to handle a different incoming request.

Echo's middleware chain also creates UAF opportunities through improper error handling. When middleware panics or returns errors, Echo's recovery mechanisms may free context objects while goroutines still hold references:

func panicUAF(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        defer func() {
            if r := recover(); r != nil {
                // Context may be partially freed during panic recovery
                logError(c, r)
            }
        }()
        
        return next(c)
    }
}

If logError captures context references asynchronously, it may access freed memory during the panic recovery phase.

Detecting Use After Free in Echo Go requires both static analysis and runtime monitoring. Static analysis tools can identify patterns where pointers escape their intended scope, while runtime tools monitor memory access patterns.

For static detection, use Go's built-in tools combined with Echo-specific analysis:

# Run Go's escape analysis to find variables that escape to heap
go build -gcflags="-m=2" ./...

# Use go vet for basic issues
go vet ./...

# Echo-specific pattern: look for context captures in goroutines
grep -r "go func()" . | grep -E "(echo\.Context|Context)"

The escape analysis output shows which variables escape to the heap, helping identify potential UAF candidates. Variables that should be stack-allocated but escape to the heap indicate possible lifetime management issues.

Runtime detection with middleBrick's API security scanner can identify UAF-related vulnerabilities in Echo Go applications through black-box testing:

npm install -g middlebrick

# Scan Echo Go API endpoint
middlebrick scan https://yourechoapi.com/api/v1

# Scan with OpenAPI spec for deeper analysis
middlebrick scan --spec openapi.yaml https://yourechoapi.com/api/v1

middleBrick tests for UAF-like patterns by sending rapid sequential requests and monitoring for inconsistent responses, memory corruption indicators, or crashes that suggest improper memory management.

For comprehensive Echo Go UAF detection, implement request correlation tracking:

type requestTracker struct {
    mu    sync.RWMutex
    ids   map[string]struct{}
}

func (rt *requestTracker) track(c echo.Context) {
    id := c.Request().Header.Get("X-Request-ID")
    rt.mu.Lock()
    rt.ids[id] = struct{}{}
    rt.mu.Unlock()
    
    // Verify no ID collision within timeout
    time.AfterFunc(100*time.Millisecond, func() {
        rt.mu.RLock()
        defer rt.mu.RUnlock()
        if _, exists := rt.ids[id]; exists {
            // Potential UAF: same ID active across requests
            log.Printf("Possible UAF: request ID %s still active", id)
        }
    })
}

This detects scenarios where Echo's context pooling might cause one request to access memory still being used by another, a common UAF symptom.

Remediating Use After Free in Echo Go requires strict adherence to Go's memory ownership rules and Echo's context lifecycle patterns. The primary principle: never capture pointers to request-scoped objects in goroutines or async operations.

Safe middleware pattern using value copying instead of pointer capture:

func safeMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // Copy values immediately, don't capture pointers
        requestID := c.Request().Context().Value("request_id")
        
        // Safe: primitive value copied, not referenced
        go func(id interface{}) {
            log.Printf("Request %v completed", id)
        }(requestID)
        
        return next(c)
    }
}

Notice how requestID is passed by value to the goroutine, ensuring the goroutine owns its copy rather than referencing potentially freed memory.

For Echo context handling, use context values instead of storing context pointers:

func contextSafe(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // Store primitive values in context, not the context itself
        c.Request().Context() = context.WithValue(
            c.Request().Context(), 
            "request_start", 
            time.Now()
        )
        
        return next(c)
    }
}

This pattern ensures you only store serializable values in context rather than pointers to Echo's internal structures.

Implement proper cleanup using Echo's middleware termination:

func cleanupMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // Use defer for cleanup to ensure execution
        defer func() {
            // Safe cleanup - no async operations
            cleanupRequestResources(c)
        }()
        
        return next(c)
    }
}

func cleanupRequestResources(c echo.Context) {
    // Release any resources held by this request
    // Echo will handle context pool cleanup automatically
}

The defer ensures cleanup happens before the function returns, preventing any access to freed memory.

For Echo applications with complex async operations, use request-scoped context cancellation:

func asyncSafe(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // Create cancellable context for this request
        ctx, cancel := context.WithCancel(c.Request().Context())
        defer cancel()
        
        // Store cancellable context in request-scoped storage
        c.Set("ctx", ctx)
        
        // Any async operations use this context
        go func(ctx context.Context) {
            select {
            case <-ctx.Done():
                // Context cancelled when request completes
                return
            case <-time.After(5 * time.Second):
                log.Println("Async operation completed safely")
            }
        }(ctx)
        
        return next(c)
    }
}

This ensures async operations are cancelled when the request completes, preventing access to freed memory.