Integer Overflow in Buffalo with Basic Auth

Integer overflow in a Buffalo application becomes significantly more dangerous when combined with HTTP Basic Authentication. Basic Auth requires the client to send credentials in the Authorization header as a base64-encoded username:password string. When Buffalo decodes this header, it typically parses the credentials into string variables. If the application then converts these strings to integers for any business logic—such as calculating offsets, buffer sizes, or loop bounds—integer overflow can occur, leading to memory corruption or unexpected behavior.

Consider a Buffalo endpoint that accepts a numeric page or limit parameter from the client. If the parameter is derived from or influenced by values embedded in the Basic Auth credentials (e.g., a tenant ID encoded in the username), an attacker can supply a large integer that overflows when added to another integer, such as an array index or a database offset. For example, if the application computes offset := page * limit and both values are derived from user-controlled inputs, an overflow can produce a very small or zero offset, causing the application to read or write memory outside intended bounds.

Because Buffalo is a Go web framework, integer overflow can result in values wrapping around, which may bypass intended validation checks. An attacker could exploit this to access unauthorized resources, trigger null pointer dereferences, or cause denial of service. The vulnerability is not in Basic Auth itself, but in how the application handles numeric conversions and arithmetic after parsing credentials. The risk is compounded when the application processes untrusted data without validating size or range, especially when the computation involves values extracted from the authenticated identity.

In the context of a black-box scan, middleBrick tests for signs of improper integer handling by sending crafted Basic Auth headers with extreme numeric values and observing application behavior. The tool does not inspect source code; instead, it infers potential overflow conditions by analyzing responses for inconsistencies, such as unexpected data exposure or errors that suggest memory corruption. When combined with other checks like Input Validation and Property Authorization, integer overflow findings are prioritized based on severity and potential impact on confidentiality and integrity.

Remediation focuses on safe parsing, strict validation, and avoiding integer arithmetic on untrusted values derived from Basic Auth. Always treat values extracted from credentials as untrusted and apply bounds checking before any conversion or computation.

Example: Unsafe parsing and arithmetic

// UNSAFE: Direct conversion and multiplication
auth := r.Header.Get("Authorization")
creds, _ := base64.StdEncoding.DecodeString(strings.TrimPrefix(auth, "Basic "))
parts := strings.Split(string(creds), ":")
page, _ := strconv.Atoi(parts[0]) // attacker-controlled
limit, _ := strconv.Atoi(parts[1]) // attacker-controlled
offset := page * limit // potential integer overflow

Example: Safe remediation with validation

// SAFE: Validate ranges and use int64 with checks
auth := r.Header.Get("Authorization")
creds, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(auth, "Basic "))
if err != nil {
    http.Error(w, "Unauthorized", http.StatusUnauthorized)
    return
}
parts := strings.Split(string(creds), ":")
if len(parts) != 2 {
    http.Error(w, "Bad Request", http.StatusBadRequest)
    return
}

page64, ok1 := new(big.Int).SetString(parts[0], 10)
limit64, ok2 := new(big.Int).SetString(parts[1], 10)
if !ok1 || !ok2 || page64.Sign() < 0 || limit64.Sign() < 0 {
    http.Error(w, "Bad Request", http.StatusBadRequest)
    return
}

// Ensure values fit into int64 and are within expected bounds
const maxLimit = 100
if page64.BitLen() > 63 || limit64.BitLen() > 63 {\n    http.Error(w, "Value too large", http.StatusBadRequest)
    return
}
page := int64(page64.Int64())
limit := int64(limit64.Int64())
if limit <= 0 || limit > maxLimit {
    http.Error(w, "Invalid limit", http.StatusBadRequest)
    return
}

// Use checked arithmetic or application-level limits
const maxOffset = 1000000
if page > (math.MaxInt64 - maxOffset) / limit {
    http.Error(w, "Invalid request", http.StatusBadRequest)
    return
}
offset := page * limit

Additional measures include using Go's math/big package for arbitrary precision when necessary, enforcing maximum limits for pagination, and avoiding the use of Basic Auth-derived values in security-sensitive arithmetic. middleBrick can verify these protections by scanning the running application with crafted credentials and inspecting responses for proper error handling and absence of anomalous behavior.