Double Free in Echo Go with Bearer Tokens

A "Double Free" in the context of Echo Go with Bearer Tokens occurs when token handling logic and HTTP request lifecycle management interact in a way that causes the same sensitive token object to be released more than once, or freed while still in use. This typically arises when middleware or handlers manipulate token pointers and the Echo framework concurrently manages request-scoped objects. Because Bearer Tokens are often stored in context values, headers, or custom request-scoped structs, incorrect reference handling can lead to use-after-free or memory corruption patterns.

Consider an Echo middleware that copies a Bearer Token from the request header into a context value for downstream handlers:

type TokenContextKey string

const TokenKey TokenContextKey = "token"

func BearerMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        token := c.Request().Header.Get("Authorization")
        // Storing a pointer to request-scoped data can be problematic
        c.Set(string(TokenKey), token)
        return next(c)
    }
}

If downstream handlers or cleanup routines free or overwrite the stored token and the same pointer is later accessed or freed again (for example, due to Echo reusing context objects across requests), a Double Free condition can manifest. This is especially risky when handlers explicitly manage memory or use Cgo to interface with libraries that perform manual allocation and deallocation of token buffers.

The interaction between Echo's routing and middleware lifecycle and the application’s token management amplifies the risk. For example, if a handler validates the token and then another middleware or a deferred cleanup function attempts to clear or free the same token pointer, the double deallocation can corrupt the runtime heap. This may lead to crashes or, in more complex deployments, provide an avenue for controlled memory manipulation. Common patterns that increase exposure include using global token caches without proper synchronization, reusing context objects across requests, or improper pointer assignments when refreshing tokens.

In security terms, this is a memory safety issue that falls under the broader category of improper resource management. While Echo Go applications are typically written in Go, which has a garbage collector, interactions with external C libraries via Cgo or unsafe memory operations can reintroduce these risks. The scanner’s checks for Unsafe Consumption and Input Validation are particularly relevant here, as they help detect insecure handling of sensitive values like Bearer Tokens.

To illustrate a vulnerable sequence: a request arrives with an Authorization header, the middleware stores the token pointer in context, a handler uses and potentially modifies the token, and a deferred function attempts to zero out or free the token. If the same pointer is referenced again later in the request lifecycle, the double free occurs. This highlights the importance of treating Bearer Tokens as immutable within the request scope and avoiding manual memory management when working with such sensitive values.

Remediation focuses on ensuring Bearer Tokens are handled as immutable values within the request lifecycle and avoiding pointer reuse or manual deallocation of token data. Instead of storing pointers to request headers or mutable buffers, store copies or structured values that do not share memory with request-scoped objects.

Here is a secure middleware pattern that copies the token value rather than storing a pointer:

type TokenContextKey string

const TokenKey TokenContextKey = "token"

func BearerMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        token := c.Request().Header.Get("Authorization")
        // Store a copy, not a pointer to request header data
        c.Set(string(TokenKey), token)
        return next(c)
    }
}

In downstream handlers, retrieve the token as a value and avoid any explicit memory operations:

func ProtectedHandler(c echo.Context) error {
    token, ok := c.Get(string(TokenKey)).(string)
    if !ok || token == "" {
        return echo.NewHTTPError(http.StatusUnauthorized, "missing token")
    }
    // Use token as a read-only value
    if !isValid(token) {
        return echo.NewHTTPError(http.StatusForbidden, "invalid token")
    }
    return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
}

If token validation requires external calls, pass the token by value to functions that do not retain references. Avoid global caches that store pointers to request-specific tokens. For structured token handling, consider using a value type:

type TokenInfo struct {
    Value string
    Scopes []string
}

func ParseToken(token string) (TokenInfo, error) {
    // Parse and return a value struct, not pointers to header data
    return TokenInfo{Value: token, Scopes: extractScopes(token)}, nil
}

When integrating with external authentication services, ensure that tokens are copied into local variables before any asynchronous or deferred operations. This prevents the accidental reuse of freed memory. The scanner’s LLM/AI Security and Input Validation checks can help identify insecure token handling patterns, while the Authentication and Property Authorization checks verify that token usage conforms to expected security controls.

Finally, leverage the CLI tool to verify your changes: use middlebrick scan <url> to confirm that the authentication findings related to Bearer Tokens are resolved. The Dashboard can then be used to track improvements over time, and the GitHub Action can enforce that no new token-related findings are introduced in pull requests.