Log Injection in Buffalo with Basic Auth

Log injection occurs when untrusted input is written directly into application or system logs without validation, encoding, or separation. In the Buffalo framework, when HTTP Basic Authentication is used, the username and password are transmitted in the Authorization header as Basic base64(credentials). If the application logs these credentials—or any part of the request derived from user-controlled data—without sanitization, an attacker can inject newline characters (\n or %0A) to forge log entries, hide malicious actions, or poison log-based monitoring pipelines.

Buffalo does not provide built-in log sanitization for authentication headers. If a developer adds custom logging around the Authorization header (for example, to audit login attempts), newline characters in the username or password can break the log format. For example, a username like admin\nContent-Security-Policy: block-all would produce two separate log lines when written naively, potentially misleading operators or log aggregation tools. In a security assessment performed by middleBrick, this pattern appears among the findings related to Data Exposure and Unsafe Consumption, because logs may inadvertently reveal credentials or be manipulated to obscure follow-up attacks.

When combined with unauthenticated or weakly authenticated endpoints, log injection in Buffalo with Basic Auth can amplify reconnaissance. An attacker can probe endpoints with crafted credentials containing payloads such as carriage returns and newlines to test whether logs are parsed correctly by SIEMs or whether injection enables log forging. middleBrick’s checks for Input Validation and Data Exposure highlight risks where authentication data is handled in logs without canonicalization. Because Basic Auth credentials are base64-encoded but not encrypted, they should never be logged in clear text; if they are, injection compounds the exposure by enabling log-based manipulation.

Remediation focuses on preventing newlines and control characters from entering loggable fields and ensuring that authentication data is never written to logs. Developers should canonicalize input by stripping or encoding newline characters before logging. MiddleBrick’s findings include prioritized guidance to remove credentials from logs and to apply strict input validation on any data that may be reflected in log output. Continuous monitoring via the Pro plan can alert teams when risky logging patterns are detected across tracked APIs.

Secure handling of Basic Authentication in Buffalo requires avoiding logging of raw credentials and ensuring that any logged values are sanitized. The following examples demonstrate safe patterns for extracting and using Basic Auth data without introducing log injection risks.

1. Do not log raw credentials. Instead, log only a hashed or redacted representation:

// Safe: log only a redacted marker, never the password
app.GET("/api/protected", func(ctx *buffalo.Context) error {
    auth := ctx.Request.Header.Get("Authorization")
    // Do NOT log auth directly
    ctx.Logger().Infof("API access attempted, auth header present: %t", auth != "")
    // Continue with authentication logic...
    return nil
})

2. If you must log authentication events, strip newlines and non-printable characters from any user-controlled data before writing to logs:

import "strings"

func sanitizeForLog(input string) string {
    // Remove newlines and carriage returns to prevent log injection
    cleaned := strings.ReplaceAll(input, "\r", "")
    cleaned = strings.ReplaceAll(cleaned, "\n", "")
    cleaned = strings.ReplaceAll(cleaned, "\u0000", "")
    return cleaned
}

app.POST("/login", func(ctx *buffalo.Context) error {
    auth := ctx.Request.Header.Get("Authorization")
    safeAuth := sanitizeForLog(auth)
    ctx.Logger().Infof("Login attempt: %s", safeAuth)
    // Perform authentication...
    return nil
})

3. Validate credentials before using them, and reject suspicious payloads early:

func isValidAuthHeader(auth string) bool {
    // Reject if contains newlines or other control characters
    if strings.ContainsAny(auth, "\r\n\u0000") {
        return false
    }
    // Additional checks, e.g., prefix and base64 format
    return strings.HasPrefix(auth, "Basic ")
}

app.GET("/api/resource", func(ctx *buffalo.Context) error {
    auth := ctx.Request.Header.Get("Authorization")
    if !isValidAuthHeader(auth) {
        ctx.Response().WriteHeader(400)
        return errors.New("invalid authorization header")
    }
    // Proceed with safe processing...
    return nil
})

4. Use middleware to centralize authentication and logging safeguards:

func BasicAuthMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        auth := r.Header.Get("Authorization")
        safeAuth := sanitizeForLog(auth)
        // Example: emit metric or audit log without raw credentials
        ctx := context.WithValue(r.Context(), "audit", safeAuth)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

// In your app initialization
app.App.Use(BasicAuthMiddleware)

These patterns ensure that log entries remain structured and that newline-based injection is not possible. When combined with middleBrick’s scans, teams can verify that authentication handling does not contribute to Data Exposure or Input Validation failures.