Header Injection in Echo Go with Basic Auth

Header Injection in the Echo Go framework when Basic Authentication is used arises when untrusted input from requests is reflected into HTTP response headers without validation or sanitization. In Echo, route handlers often read headers, query parameters, or form values and then set custom headers in the response using ctx.Response().Header().Set(). If these values originate from user-controlled sources and are concatenated into header values, an attacker can inject additional header lines.

Basic Auth typically involves an Authorization header with the prefix Basic followed by base64-encoded username:password. While the decoding and validation step itself does not directly enable injection, the pattern of treating the extracted identity (username) as a downstream header value can create risks. For example, a developer might extract the Basic Auth username and forward it into a custom header such as X-User-ID or X-Forwarded-For without sanitization. If the username contains carriage returns or line feeds (CRLF characters, represented as %0d%0a or literal \r\n), these can break the header structure and allow injection of new headers like Set-Cookie or Location.

Echo Go applications that combine Basic Auth extraction with dynamic header setting are vulnerable when:

• User-controlled data (including decoded credentials or derived fields) is placed into response headers without strict allowlisting or sanitization.
• The framework or middleware does not enforce canonical header formatting, allowing multiple headers with the same name via injected CRLF sequences.
• Logging or debugging features inadvertently reflect header values without encoding, aiding attacker reconnaissance for injection attempts.

An attacker can exploit this to inject malicious headers such as Set-Cookie: session=hijacked or manipulate caching and redirection behavior via Location injection. In the context of an OpenAPI/Swagger specification analyzed by middleBrick, such flaws may appear as missing validation on header fields or overly permissive schema definitions that do not restrict character sets. Runtime probing may then detect reflected header inconsistencies or missing input validation, which are surfaced as findings with remediation guidance to enforce strict validation and avoid reflecting raw user input into headers.

To remediate Header Injection when using Basic Auth in Echo Go, ensure that any data derived from authentication is treated as untrusted and never directly reflected into HTTP response headers. Apply strict validation, avoid concatenating raw values into headers, and use framework features that enforce safe header handling.

Example of vulnerable code:

// Vulnerable: directly using Basic Auth username in a custom header
func handler(c echo.Context) error {
    user, pass, ok := c.Request().BasicAuth()
    if !ok {
        return echo.ErrUnauthorized
    }
    // Unsafe: user may contain CRLF
    c.Response().Header().Set("X-User-Name", user)
    return c.String(http.StatusOK, "Hello")
}

Remediated code:

// Safe: validate and sanitize before using in headers
func handler(c echo.Context) error {
    user, pass, ok := c.Request().BasicAuth()
    if !ok {
        return echo.ErrUnauthorized
    }
    // Validate username format: allow only alphanumeric, underscore, hyphen
    if !regexp.MustCompile(`^[A-Za-z0-9_-]+$`).MatchString(user) {
        return echo.ErrBadRequest
    }
    // Safe: set header with validated value
    c.Response().Header().Set("X-User-Name", user)
    return c.String(http.StatusOK, "Hello")
}

Additional protective measures include:

• Never setting headers from raw query parameters or form fields that may originate from the same request as Basic Auth credentials.
• Using middleware to normalize and sanitize headers globally, ensuring that any user-influenced data is either removed or encoded (e.g., replacing CRLF with safe placeholders) before being set.
• Leveraging Echo’s built-in security middleware where available to enforce content security policies and restrict header manipulation.

When using the middleBrick CLI (middlebrick scan <url>) or integrating the GitHub Action to add API security checks to your CI/CD pipeline, scans will flag header injection risks and map findings to frameworks such as OWASP API Top 10, providing prioritized remediation guidance rather than attempting to fix the issue automatically.