Stack Overflow in Echo Go with Basic Auth

When an Echo Go service uses HTTP Basic Authentication and is susceptible to a stack overflow, the combination can amplify risk by exposing both authentication handling and memory-safety bugs in the same request path. Basic Auth in Echo Go typically involves extracting the Authorization header, decoding the base64 credentials, and validating them before proceeding to route handlers.

During this flow, unsafe parsing of headers or credentials—such as repeated string concatenation, unchecked input lengths, or improper use of byte buffers—can trigger a stack overflow. An attacker can send a long or malformed Authorization header (e.g., a very long base64 string or deeply nested encoded payload) that causes the stack to exhaust its memory during decoding or comparison. This can lead to a crash or, in some configurations, arbitrary code execution depending on the runtime and memory layout.

Because middleBrick scans unauthenticated attack surfaces, it can detect indicators such as missing length limits on headers, absence of size checks on the Authorization value, and patterns that suggest unsafe handling of credentials. A scan of an Echo Go endpoint using Basic Auth without input validation or rate limiting may surface findings related to Input Validation, Authentication, and potentially Data Exposure if credentials are mishandled during processing.

For example, an Echo Go route like the following can be risky if the header value is not bounded:

c := echo.New()
c.GET("/protected", func(ctx echo.Context) error {
    auth := ctx.Request().Header.Get("Authorization")
    if auth == "" {
        return echo.ErrUnauthorized
    }
    // naive parsing: vulnerable to long input
    parts := strings.Split(auth, " ")
    if len(parts) != 2 || parts[0] != "Basic" {
        return echo.ErrUnauthorized
    }
    decoded, err := base64.StdEncoding.DecodeString(parts[1])
    if err != nil {
        return echo.ErrUnauthorized
    }
    creds := string(decoded)
    // unsafe credential handling
    if creds != "admin:secret" {
        return echo.ErrUnauthorized
    }
    return ctx.String(http.StatusOK, "OK")
})

In this pattern, parts[1] can be arbitrarily large, and base64 decoding may expand or consume stack memory in ways that are not immediately obvious, especially if the runtime or libraries involved have nuanced memory handling. A scanner that tests for missing input validation and excessive data exposure would flag this as a high-risk pattern.

To secure Basic Auth in Echo Go, enforce strict limits on header size, validate format early, and avoid unsafe string and byte operations that can contribute to stack-related issues. Use bounded buffers and standard library functions that handle memory safely.

Here is a safer implementation that includes header length checks, controlled base64 decoding, and constant-time comparison where feasible:

c := echo.New()
c.Pre(middleware.RequestWithConfig(middleware.RequestConfig{
    Skipper: func(e echo.Context) bool {
        return false
    },
    BeforeFunc: func(next echo.HandlerFunc) echo.HandlerFunc {
        return func(ctx echo.Context) error {
            auth := ctx.Request().Header.Get("Authorization")
            if len(auth) > 1024 {
                return echo.ErrUnauthorized
            }
            if !strings.HasPrefix(auth, "Basic ") {
                return echo.ErrUnauthorized
            }
            token := auth[len("Basic "):]
            if len(token) == 0 {
                return echo.ErrUnauthorized
            }
            decoded, err := base64.StdEncoding.DecodeString(token)
            if err != nil {
                return echo.ErrUnauthorized
            }
            // limit decoded length to avoid excessive memory use
            if len(decoded) > 256 {
                return echo.ErrUnauthorized
            }
            // constant-time check can be approximated by using hmac
            expected := []byte("admin:secret")
            if subtle.ConstantTimeCompare(decoded, expected) != 1 {
                return echo.ErrUnauthorized
            }
            ctx.Set("user", string(decoded))
            return next(ctx)
        }
    },
}))

c.GET("/protected", func(ctx echo.Context) error {
    return ctx.String(http.StatusOK, "OK")
})

Key improvements include:

• Length check on the raw Authorization header to prevent oversized inputs that may stress the stack during processing.
• Strict prefix validation and early rejection of malformed schemes.
• Limit on decoded credential length to avoid unbounded memory use.
• Use of subtle.ConstantTimeCompare to reduce timing side-channels when comparing credentials.

Additionally, enable request size limits at the server level and consider rejecting requests with unusually long headers before they reach application logic. These steps reduce the likelihood of stack overflow conditions and align with secure handling of credentials in HTTP Basic Auth flows.