Log Injection in Echo Go with Basic Auth

Log injection occurs when untrusted data is written directly into application logs without sanitization, enabling log forging or log poisoning attacks. In Echo Go, combining user-controlled input with Basic Authentication headers can produce log entries that mix attacker-controlled data with server-generated metadata, creating an injection surface.

Consider an Echo handler that authenticates via Basic Auth and then logs the username extracted from the Authorization header. If the username contains newline characters or structured delimiters, a single log line can be transformed into multiple fabricated entries. For example, a username like alice\n"EVIL" can cause the log to appear as two separate events, which can be exploited during incident investigation or SIEM parsing. An attacker may inject fabricated timestamps, severity labels, or key-value pairs that mimic legitimate events, reducing the reliability of audit trails.

Echo’s default logging behavior does not sanitize incoming request metadata. When Basic Auth credentials are decoded and written into logs verbatim, newlines in the username or password fields directly corrupt the log structure. This is especially relevant when credentials are reused across services and logs are aggregated centrally. The resulting log forging can obscure real attacks or fabricate false positives, complicating forensic analysis.

Additionally, path traversal or query parameters that are logged without sanitization can interact with Basic Auth–based session handling, leading to injection across multiple dimensions. For instance, logging the request URI while also logging the authenticated user can produce entries that appear to originate from a different identity. Attackers may use crafted payloads to test for log injection by sending requests with malformed credentials and inspecting log outputs for unexpected line breaks or injected fields.

Because middleBrick scans unauthenticated attack surfaces, it can detect indicators of log injection by observing responses that echo credentials or by analyzing whether log-like responses contain structured log patterns. However, middleBrick does not fix the issue; it reports findings with remediation guidance so teams can harden logging practices.

To mitigate log injection when using Basic Auth in Echo Go, avoid directly logging raw credential values and sanitize all user-controlled data before it reaches the logging layer. Prefer structured logging with explicit field separation and ensure that newlines and other control characters are either removed or escaped.

Below is a secure example that decodes Basic Auth, validates the username, and logs using a structured logger that does not concatenate raw input into a free-text message.

package main

import (
	"net/http"
	"strings"

	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
	"go.uber.org/zap"
)

var logger, _ = zap.NewProduction()
	ype safeUser struct {
	username string
}

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

func basicAuthMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		user, pass, ok := c.Request().BasicAuth()
		if !ok {
			return c.String(http.StatusUnauthorized, "authorization required")
		}
		// Validate and sanitize before logging
		safeUsername := sanitizeUsername(user)
		if safeUsername == "" {
			return c.String(http.StatusBadRequest, "invalid user")
		}
		logger.Info("basic_auth_attempt",
			zap.String("username", safeUsername),
			zap.String("source_ip", c.RealIP()),
		)
		c.Set("user", safeUser{username: safeUsername})
		return next(c)
	}
}

func helloHandler(c echo.Context) error {
	if usr, ok := c.Get("user").(safeUser); ok {
		return c.String(http.StatusOK, "welcome, "+usr.username)
	}
	return c.String(http.StatusInternalServerError, "internal error")
}

func main() {
	e := echo.New()
	e.Use(middleware.LoggerWithConfig(middleware.LoggerConfig{
		Format: "method=${method}, uri=${uri}, status=${status}",
	}))
	e.Use(basicAuthMiddleware)
	e.GET("/", helloHandler)
	e.Logger.Fatal(e.Start(":8080"))
}

Key remediation steps encoded in this example:

• Decode credentials via c.Request().BasicAuth() rather than parsing headers manually.
• Sanitize the username by removing newline and carriage return characters before it is used in any log line.
• Use structured logging with explicit key-value pairs (e.g., zap.String) to avoid concatenating raw input into a message template.
• Do not log the password under any circumstances; only log necessary metadata like the sanitized username and source IP.

Alternative mitigations include rejecting credentials that contain control characters at the validation layer and enforcing a strict character whitelist for usernames. These measures reduce the likelihood that injected content can alter the structure of logs ingested by external analysis tools.