Use After Free in Echo Go with Hmac Signatures

Use After Free (UAF) occurs when memory is freed but subsequent code continues to reference it. In Echo Go, combining Hmac signature validation with improper memory handling can expose UAF when request context is reused or released prematurely. Consider an HTTP handler that parses a JSON payload, generates an Hmac signature over selected headers, and then conditionally frees or reuses the underlying byte buffer based on signature checks.

Example vulnerable pattern in Echo Go:

c := contextPool.Get().(*RequestContext)
defer contextPool.Put(c)
bodyBytes, _ := io.ReadAll(c.Request().Body)
sig := c.Request().Header.Get("X-Signature")
valid := verifyHmac(bodyBytes, sig)
if !valid {
    contextPool.Put(nil) // early "free"
    echo.NewHTTPError(401).SetInternalMessage("invalid signature")
    return
}
// Use c after potential free
process(c.Request().Body) // UAF if context was returned to pool and reused

In this pattern, if the context is returned to a pool or freed early, later use of c.Request().Body can reference already-freed memory. Because Hmac signature verification occurs before any guarded cleanup, an attacker can manipulate control flow (for example, by sending a short-circuit invalid signature) to trigger the early path that releases the context, while a separate execution thread or reused object still holds a reference. This mismatch between signature validation timing and memory lifecycle creates a Use After Free window.

Another scenario involves signature computation on a shared buffer. If you compute Hmac over a mutable byte slice and then release the slice while an in-flight goroutine or deferred function still holds a pointer, the freed memory may be reallocated for attacker-controlled content. Echo Go’s fast request handling can exacerbate this when handlers share buffers via context or global sync pools, and the Hmac check does not guarantee the buffer remains pinned for the entire handler lifetime.

Real-world parallels exist in C-based servers where signature verification is done on a parsed object that is later destroyed; in Go, the risk manifests through improper pooling or premature release rather than explicit free calls. The OWASP API Top 10 category “2023-A01: Broken Access Control” can intersect here if object reuse allows unauthorized access, while the broader class of memory safety issues aligns with common implementation weaknesses that security scanners flag.

To prevent Use After Free in Echo Go with Hmac signatures, ensure the request context and any buffers it references remain valid for the entire handler execution and are not returned to a pool or overwritten prematurely. Use explicit ownership semantics: do not early-free shared objects, and avoid returning contexts to a pool when early exits occur.

Remediated code example:

c := contextPool.Get().(*RequestContext)
if c == nil {
    c = &RequestContext{}
}
// Ensure cleanup happens only after all uses
defer func() {
    cleanupContext(c)
    contextPool.Put(c)
}()
bodyBytes, err := io.ReadAll(c.Request().Body)
if err != nil {
    echo.NewHTTPError(400, "failed to read body")
    return
}
sig := c.Request().Header.Get("X-Signature")
if !verifyHmac(bodyBytes, sig) {
    echo.NewHTTPError(401, "invalid signature")
    return
}
// Safe to use c and its body here; deferred cleanup runs after processing
process(c.Request().Body)

This pattern guarantees that the context is not returned to the pool until after all operations that depend on it complete. The defer ensures cleanup and release happen in a single, predictable scope, eliminating the window where a pointer could dangle.

When computing Hmac over mutable buffers, copy the data if you must release the source early:

bodyBytes, _ := io.ReadAll(c.Request().Body)
sig := c.Request().Header.Get("X-Signature")
if !verifyHmac(bodyBytes, sig) {
    // bodyBytes is local and will be garbage collected; no reuse
    echo.NewHTTPError(401, "invalid signature")
    return
}
// Make a copy if you need to hand off to another goroutine
copied := make([]byte, len(bodyBytes))
copy(copied, bodyBytes)
go func(payload []byte) {
    // process copy, original buffer can be released immediately
    worker(payload)
}(copied)
// Original bodyBytes can go out of scope safely

For integration with the broader ecosystem, the CLI tool can be used to scan your handlers: middlebrick scan <url>. If you automate checks, the GitHub Action can fail builds when risk scores degrade, and the MCP Server lets you scan APIs directly from your AI coding assistant to catch such patterns early.

Finally, align remediation with framework mappings. Findings can reference OWASP API Top 10 and guidance for secure memory handling. The Pro plan supports continuous monitoring so repeated instances are caught across deployments, and compliance reports can map these controls to relevant standards.