Stack Overflow in Echo Go with Api Keys

A Stack Overflow in an Echo Go service that uses API keys occurs when user-controlled input that includes an API key is processed without length or structure validation, and then used in a way that leads to unbounded memory consumption or deep recursive calls. In Echo Go, this commonly arises when the API key is accepted via headers or query parameters and then forwarded into logging, telemetry, or downstream request construction without sanitization or size limits.

Consider an Echo handler that receives an API key via the X-API-Key header and passes it into a context value for downstream middleware or logging:

c.Set("apiKey", c.Request().Header.Get("X-API-Key"))

If an attacker sends an extremely long X-API-Key value, Echo Go may allocate large buffers to hold the header, potentially triggering a stack growth path or repeated allocations that culminate in a stack overflow or out-of-memory condition. This becomes more likely when additional processing (e.g., base64 decoding, HMAC verification, or recursive middleware traversal) is applied to the key without input validation.

Another scenario involves response headers that echo the API key, for example in debug or authentication failure responses. If the API key is reflected into headers or logs without truncation or encoding, and the client or a downstream proxy treats it as structured data, it may cause parsing paths to grow unbounded, leading to resource exhaustion that resembles a stack overflow pattern.

When using API keys for authentication, ensure that validation occurs early and that the key’s length and format are constrained before it touches any processing or logging paths. Echo Go applications should treat API keys as untrusted input and apply strict boundaries to prevent resource exhaustion paths that can be triggered by oversized or malformed keys.

Remediation focuses on input validation, bounded copying, and avoiding unnecessary propagation of raw API keys within application structures. In Echo Go, validate and constrain API keys before they are stored in contexts or used in downstream logic.

1) Validate length and format early in a middleware, and reject clearly malformed keys:

const maxAPIKeyLength = 512

func APIKeyMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        key := c.Request().Header.Get("X-API-Key")
        if key == "" {
            return echo.NewHTTPError(http.StatusUnauthorized, "missing api key") // 401
        }
        if len(key) > maxAPIKeyLength {
            return echo.NewHTTPError(http.StatusBadRequest, "api key too long") // 400
        }
        if !isValidAPIKeyFormat(key) {
            return echo.NewHTTPError(http.StatusBadRequest, "invalid api key format") // 400
        }
        // Store only a safe, bounded copy
        safeKey := key[:min(len(key), 256)]
        c.Set("apiKeySafe", safeKey)
        return next(c)
    }
}

func isValidAPIKeyFormat(key string) bool {
    // Example: allow alphanumeric and limited punctuation
    for _, r := range key {
        if !(r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' || r == '-' || r == '_') {
            return false
        }
    }
    return true
}

func min(a, b int) int {
    if a < b {
        return a
    }
    return b
}

This ensures the key is checked for size and character constraints, and only a bounded copy is stored in the context, reducing the risk of unbounded memory use.

2) Avoid echoing raw API keys in logs or headers. If you must include a key for traceability, truncate and hash it:

import "crypto/sha256"
import "encoding/hex"

func safeLogAPIKey(key string) string {
    if len(key) == 0 {
        return "[none]"
    }
    h := sha256.Sum256([]byte(key))
    return hex.EncodeToString(h[:])[:16] // truncated hash for traceability
}

// Usage in logging:
log.Printf("request api_key_hash=%s method=%s path=%s", safeLogAPIKey(c.Get("apiKeySafe".(string))), c.Request().Method, c.Request().RequestURI)

3) When constructing outbound requests that require the API key, avoid unbounded concatenation or deep copying of user-controlled values. Use fixed-size buffers or explicit size checks:

func buildUpstreamRequest(apiKey string, baseURL string) (*http.Request, error) {
    if len(apiKey) == 0 {
        return nil, errors.New("missing api key")
    }
    req, err := http.NewRequest(http.MethodGet, baseURL, nil)
    if err != nil {
        return nil, err
    }
    req.Header.Set("X-API-Key", apiKey)
    // Ensure header size remains reasonable
    if len(req.Header.Get("X-API-Key")) > 1024 {
        return nil, errors.New("api key header too large")
    }
    return req, nil
}

By validating, bounding, and minimizing the exposure of API keys in both inbound and outbound paths, you reduce the conditions that can lead to stack-related resource exhaustion in Echo Go services.