Integer Overflow in Echo Go with Basic Auth

An integer overflow in an Echo Go service that uses HTTP Basic Authentication can occur when user-controlled numeric values (e.g., Content-Length, parsed integers from headers or query parameters, or buffer sizes) are processed without proper bounds checking. In Go, arithmetic operations like addition or multiplication on fixed-size numeric types (e.g., int, uint32) silently wrap on overflow, producing a small resulting value rather than an error. When such a value is used to allocate buffers or determine slice lengths, the resulting allocation may be far smaller than expected, leading to buffer overflows or out-of-bounds writes during subsequent operations.

Basic Authentication introduces a specific vector when credentials are parsed and decoded. An attacker can supply a long Base64-encoded Authorization header that, once decoded, yields a large combined username:password string. If the server decodes this value and uses arithmetic to compute lengths or indexes (for example, to split on ':' or to copy into fixed-size buffers), an integer overflow in those calculations can misrepresent the true size. Because the request is unauthenticated, middleBrick’s unauthenticated scan surface includes the Basic Auth handling path, and the decoder logic becomes reachable without credentials, increasing exposure.

Consider an endpoint that reads a numeric header X-Item-Count, decodes Basic Auth, and computes a total buffer size as count * 256 + len(decodedCredentials). If X-Item-Count is large enough that count * 256 overflows a 32-bit integer, the total size may become small. The subsequent allocation undershoots the real data needs, and a copy operation can overflow the backing array. MiddleBrick checks such unauthenticated paths for input validation and unsafe consumption issues, highlighting how malformed or extreme values can propagate through arithmetic into memory safety problems.

Real-world patterns mirror known issues like CVE-2021-33517, where incorrect length calculations led to buffer overflows. In Echo Go, this often maps to the Input Validation and Unsafe Consumption checks, which inspect how numeric inputs from headers, query strings, and parsed credentials are sanitized before use. Even without authentication, the Basic Auth header is part of the unauthenticated attack surface, so flaws in its parsing and arithmetic usage are detectable by middleBrick’s 12 parallel security checks.

To illustrate, the following Echo Go snippet demonstrates vulnerable arithmetic and credential handling:

// Vulnerable: integer overflow risk with Basic Auth parsing
func handler(c echo.Context) error {
    auth := c.Request().Header.Get("Authorization")
    // Basic Auth format: "Basic base64(credentials)"
    const prefix = "Basic "
    if !strings.HasPrefix(auth, prefix) {
        return echo.NewHTTPError(http.StatusUnauthorized)
    }
    encoded := strings.TrimPrefix(auth, prefix)
    decoded, err := base64.StdEncoding.DecodeString(encoded)
    if err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid auth")
    }
    // Assume format username:password
    parts := bytes.SplitN(decoded, []byte{':'}, 2)
    if len(parts) != 2 {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid credentials")
    }
    username := parts[0]
    password := parts[1]

    // Risky arithmetic: user-controlled count combined with credential length
    countStr := c.QueryParam("count")
    count, err := strconv.Atoi(countStr)
    if err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "count invalid")
    }
    total := count*256 + len(username) + len(password) // potential integer overflow
    buf := make([]byte, total)                        // undersized allocation if overflow
    // Further processing may copy more data than buf can hold
    return c.JSON(map[string]interface{}{"ok": true})
}

In this example, if count is large (e.g., near the max int for the platform), the expression count*256 + len(username) + len(password) can overflow, yielding a small total. The buffer allocation then becomes too small, yet subsequent copy operations may assume a larger size, risking memory corruption. MiddleBrick’s checks flag such patterns, emphasizing input validation and safer arithmetic (e.g., using uint64 with explicit overflow checks or math/bits APIs) before using computed sizes in memory operations.

Remediation centers on avoiding arithmetic with untrusted lengths and ensuring allocations match actual data sizes. Validate and bound numeric inputs before using them in calculations. Use types with larger ranges where appropriate, and check for overflow explicitly using functions from the math package or by pre-checking against maximum safe values. When handling Basic Auth, avoid relying on decoded credential lengths in arithmetic; instead, use fixed-size buffers or streaming approaches that do not require size multiplication.

Below are concrete, secure code examples for Echo Go that address the integer overflow risk in the presence of Basic Authentication.

1) Validate and bound inputs, use explicit overflow checks:

// Secure: bounded count and overflow-safe total calculation
func handler(c echo.Context) error {
    auth := c.Request().Header.Get("Authorization")
    const prefix = "Basic "
    if !strings.HasPrefix(auth, prefix) {
        return echo.NewHTTPError(http.StatusUnauthorized)
    }
    encoded := strings.TrimPrefix(auth, prefix)
    decoded, err := base64.StdEncoding.DecodeString(encoded)
    if err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid auth")
    }
    parts := bytes.SplitN(decoded, []byte{':'}, 2)
    if len(parts) != 2 {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid credentials")
    }

    countStr := c.QueryParam("count")
    count, err := strconv.Atoi(countStr)
    if err != nil || count < 0 || count > 1024 { // enforce reasonable bound
        return echo.NewHTTPError(http.StatusBadRequest, "count out of range")
    }

    // Use uint64 for overflow-safe computation
    const factor = 256
    if count > (math.MaxUint64-factor) / factor {
        return echo.NewHTTPError(http.StatusRequestEntityTooLarge, "count too large")
    }
    total := uint64(count)*factor + uint64(len(parts[0])) + uint64(len(parts[1]))
    if total > 10<<20 { // e.g., cap at 10 MiB
        return echo.NewHTTPError(http.StatusRequestEntityTooLarge, "total size too large")
    }
    buf := make([]byte, total) // allocation matches computed size
    // Process data without risky multiplications on untrusted values
    return c.JSON(map[string]interface{}{"ok": true})
}

2) Avoid length-based multiplication entirely; use streaming or fixed buffers:

// Secure: stream processing without large computed buffers
func handler(c echo.Context) error {
    auth := c.Request().Header.Get("Authorization")
    const prefix = "Basic "
    if !strings.HasPrefix(auth, prefix) {
        return echo.NewHTTPError(http.StatusUnauthorized)
    }
    encoded := strings.TrimPrefix(auth, prefix)
    decoded, err := base64.StdEncoding.DecodeString(encoded)
    if err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid auth")
    }
    // Process decoded data in chunks rather than computing total size
    reader := bytes.NewReader(decoded)
    buf := make([]byte, 256)
    for {
        n, err := reader.Read(buf)
        if n > 0 {
            // process chunk
            _ = buf[:n]
        }
        if err == io.EOF {
            break
        }
        if err != nil {
            return echo.NewHTTPError(http.StatusInternalServerError, "read error")
        }
    }
    return c.JSON(map[string]interface{}{"ok": true})
}

These patterns ensure that numeric inputs are bounded, overflow checks are explicit, and memory allocations remain proportional to actual data sizes. Basic Auth handling remains part of the unauthenticated surface scanned by middleBrick, so applying these fixes reduces findings in Input Validation and Unsafe Consumption categories.