Memory Leak in Buffalo with Hmac Signatures

A memory leak in a Buffalo application that uses Hmac Signatures typically arises when request data and cryptographic context are retained longer than necessary. In Buffalo, each incoming request is handled by a controller action. If you compute an Hmac Signature on request parameters or a payload and store intermediate buffers, maps, or custom signer objects in request-scoped variables that are referenced elsewhere (for example, in closures attached to background jobs or in global caches), the garbage collector may not reclaim that memory promptly. This becomes more likely when the signature logic creates large byte slices, repeatedly allocates new hash instances, or when the application caches request-specific state across requests.

Consider a scenario where a handler builds a signature string and attaches it to a context value or a session map that is retained for logging or replay detection. If the data includes large file uploads or many form fields, the underlying byte arrays and associated structures may remain referenced, preventing reclamation. In concurrent workloads, repeated allocations for each signed request can increase pressure on the garbage collector, leading to higher memory usage over time. While this pattern does not directly expose secrets, it can degrade service stability and indirectly aid an attacker by making the service more susceptible to resource exhaustion or side-channel conditions that complicate normal monitoring.

Using middleBrick to scan such an API can surface related findings. For instance, one of the 12 security checks, Unsafe Consumption, may flag unexpected data retention or missing limits on request payload size when the scanner observes large inputs being processed without clear bounds. Similarly, the Inventory Management and Property Authorization checks can highlight endpoints where request state is handled inconsistently, increasing the chance of unintended retention. Although the scanner does not fix the leak, its prioritized findings and remediation guidance can steer developers toward safer patterns like strict size limits, short-lived contexts, and avoiding global caches for request-specific signatures.

To mitigate memory concerns while using Hmac Signatures in Buffalo, structure your code to minimize retained state and ensure allocations are short-lived. Use fixed-size buffers where possible, avoid attaching large intermediate objects to long-lived contexts, and prefer streaming or single-pass hashing for large payloads. Below are concrete, working examples that demonstrate secure handling in a Buffalo controller.

Example 1: Stateless signature verification without retaining request data

// handlers/signatures.go
package handlers

import (
    "crypto/hmac"
    "crypto/sha256"
    "net/http"

    "github.com/gobuffalo/buffalo"
)

func VerifyWebhook(c buffalo.Context) error {
    payload := c.Request().Body
    signatureHeader := c.Request().Header.Get("X-Signature-256")
    if signatureHeader == "" {
        return c.Error(http.StatusBadRequest, errors.New("missing signature"))
    }

    key := []byte("your-256-bit-secret-key-must-be-secure-and-rotated")
    mac := hmac.New(sha256.New, key)
    // Read the body once; avoid storing the full payload in memory longer than needed
    buf := make([]byte, 4096)
    totalWritten := 0
    for {
        n, err := payload.Read(buf)
        if n > 0 {
            mac.Write(buf[:n])
            totalWritten += n
        }
        if err != nil {
            break
        }
    }
    expectedMAC := mac.Sum(nil)
    if !hmac.Equal(expectedMAC, []byte(signatureHeader)) {
        return c.Error(http.StatusUnauthorized, errors.New("invalid signature"))
    }

    // Process only after verification; do not keep a copy of raw body in context
    c.Set("verified", true)
    return c.Render(200, r.JSON(map[string]bool{"verified": c.Get("verified").(bool)}))
}

Example 2: Signed response generation with bounded allocations

// handlers/signatures.go
package handlers

import (
    "crypto/hmac"
    "crypto/sha256"
    "encoding/hex"
    "net/http"

    "github.com/gobuffalo/buffalo"
)

func GenerateSignedResponse(c buffalo.Context) error {
    payload := c.Param("data")
    key := []byte("your-256-bit-secret-key-must-be-secure-and-rotated")

    mac := hmac.New(sha256.New, key)
    mac.Write([]byte(payload))
    signature := hex.EncodeToString(mac.Sum(nil))

    // Avoid attaching large or repeated objects to the context; keep only essentials
    resp := map[string]string{
        "data": payload,
        "sig":  signature,
    }
    return c.Render(200, r.JSON(resp))
}

Operational guidance

• Limit request body size globally or per-route to prevent unbounded memory growth.
• Do not store computed signatures or hashed objects in long-lived caches keyed by request identifiers.
• Use hmac.Equal for constant-time comparison to avoid timing-based side channels.
• If you use background jobs, serialize only necessary data and avoid embedding large buffers or contexts.

These patterns reduce the likelihood of memory retention and keep allocations predictable. When combined with scans via middleBrick — for example, using the CLI (middlebrick scan <url>) or the GitHub Action to enforce risk thresholds — teams can detect related anomalies early and iteratively improve handling of Hmac Signatures in production workloads.