Integer Overflow in Echo Go with Bearer Tokens

Integer overflow in an Echo Go API that uses Bearer tokens can occur when user-controlled numeric inputs (e.g., quantity, size, or iteration counts derived from request parameters or headers) are used in arithmetic without range validation. An attacker can supply values like math.MaxUint32 + 1, causing wrap-around to small or zero values, which may bypass size checks, trigger negative interpretations, or lead to buffer underflows/overflows in downstream processing.

When combined with Bearer tokens, the risk chain typically involves:

• Authentication via Authorization: Bearer <token> header parsing and validation.
• Business logic that uses parsed header or token claims (e.g., scopes or tenant IDs) in numeric operations such as pagination offsets, buffer allocations, or loop bounds.
• An unauthenticated or weakly validated endpoint where an attacker can send crafted integers alongside a valid Bearer token, or exploit token parsing to inject malicious numeric values.

For example, if an endpoint decodes a Bearer token and extracts a numeric claim (like org_id) to compute a memory offset or a loop limit, an oversized integer can wrap and produce an invalid offset, leading to memory corruption or information disclosure. In Echo Go, common triggers include unchecked conversions from string to uint64, int addition without saturation, and misuse of middleware counters that rely on token-derived identifiers.

Real-world patterns mirror known CWEs such as CWE-190 (Integer Overflow or Wraparound) and CWE-130 (Improper Validation of Array Index). In the context of OWASP API Top 10, this aligns with Broken Function Level Authorization and Excessive Data Exposure when overflow leads to bypassing access controls or exposing sensitive memory.

Consider an Echo Go handler that computes a buffer size from a query parameter and a token-derived multiplier:

// Risky: integer overflow when tokenMultiplier and userSize are large
tokenMultiplier := getUserMultiplier(c.Get("tenant_id")) // derived from token claim
userSize, _ := strconv.ParseUint(c.QueryParam("size"), 10, 64)
bufferSize := uint64(tokenMultiplier) * userSize // may overflow
buf := make([]byte, bufferSize) // panic or truncation

If an attacker provides size=math.MaxUint64 and the token claim yields multiplier=2, the multiplication wraps, producing a tiny buffer that leads to unsafe slicing. Even if the API returns a 500, side effects such as panics or inconsistent state may leak behavior useful for further attacks.

Using OpenAPI/Swagger spec analysis, middleBrick correlates numeric parameter definitions with runtime inputs and token claim usage, highlighting mismatches where unchecked arithmetic intersects with authenticated contexts. This helps identify endpoints where Bearer token data flows into integer operations without bounds checks.

Remediation focuses on validating and sanitizing integer inputs before arithmetic, using safe types and checks, and isolating token-derived values from unchecked computations. Below are concrete, secure patterns for Echo Go handlers that use Bearer tokens.

1. Validate and bound integer inputs

Always parse user inputs with explicit range checks. Use strconv.ParseUint with bit size and verify against business limits.

size, err := strconv.ParseUint(c.QueryParam("size"), 10, 32) // limit to 32-bit
if err != nil || size > 10_000 {
    echoErr(c, "invalid size", http.StatusBadRequest)
    return
}

2. Avoid wrapping multiplication with saturated or checked arithmetic

Use explicit checks before multiplication or use libraries that provide safe math. In pure Go, pre-check products against MaxUint64.

const maxBufferSize = 32 << 20 // 32 MB cap
multiplier := uint64(getTenantMultiplier(c.Get("tenant_id")))
if multiplier == 0 || size > maxBufferSize/multiplier {
    echoErr(c, "buffer size too large", http.StatusBadRequest)
    return
}
bufferSize := multiplier * size

3. Isolate token-derived values from arithmetic

Do not directly use claims from Bearer tokens in memory allocations or loop bounds. Map claims to validated enums or small integers via a lookup table.

// Safe mapping instead of raw claim usage
tenantMultipliers := map[string]uint64{
    "small":  1,
    "medium": 2,
    "large":  4,
}
token := c.Get("tenant_id").(string) // after type assertion
mult, ok := tenantMultipliers[token]
if !ok || size > maxBufferSize/mult {
    echoErr(c, "access denied or invalid parameters", http.StatusForbidden)
    return
}
bufferSize := mult * size

4. Use context timeouts and request scope limits

Even with correct arithmetic, cap processing time and memory. Echo provides request-scoped cancellation and context values to enforce limits.

ctx, cancel := context.WithTimeout(c.Request().Context(), 5*time.Second)
defer cancel()
c.SetRequest(c.Request().WithContext(ctx))
// Use context-aware database or HTTP calls downstream

5. Secure Bearer token parsing and middleware

Ensure token extraction and validation do not introduce integer conversions. Keep token handling minimal and avoid embedding numeric data in tokens that drive arithmetic.

auth := c.Request().Header.Get("Authorization")
if auth == "" {
    echoErr(c, "missing authorization", http.StatusUnauthorized)
    return
}
const bearerPrefix = "Bearer "
if !strings.HasPrefix(auth, bearerPrefix) {
    echoErr(c, "invalid authorization format", http.StatusUnauthorized)
    return
}
token := strings.TrimPrefix(auth, bearerPrefix)
// Validate token via middleware; do not derive integers directly from it
claims, err := verifyToken(token)
if err != nil {
    echoErr(c, "invalid token", http.StatusUnauthorized)
    return
}
c.Set("tenant_id", claims["tenant"])

Comparison of approaches

By combining input validation, bounded arithmetic, and secure token handling, Echo Go services can mitigate integer overflow risks even when Bearer tokens carry claims that influence numeric operations. middleBrick can support this posture by scanning endpoints to detect unchecked integer operations and mapping them to relevant compliance rules such as OWASP API Top 10 and relevant CVEs.