Session Fixation in Echo Go with Basic Auth

Session fixation occurs when an application assigns a user a session identifier before authentication and does not issue a new identifier after authentication. In Echo Go, if Basic Auth is used without regenerating session tokens, an attacker can set a known session cookie for the victim, authenticate with their own credentials, and inherit the same session, effectively impersonating the victim. This combination is risky because Basic Auth typically relies on repeated transmission of credentials (username:password in an Authorization header), and if the application also uses session cookies, failing to rotate the session after successful authentication can link the attacker’s pre‑chosen session to the authenticated user.

Consider an Echo Go service that uses a session cookie to track authenticated state while also validating Basic Auth on each request. If the login handler only validates credentials and does not call a session regeneration function, the session cookie remains the one the attacker forced the victim to use. MiddleBrick’s checks for BOLA/IDOR and Unsafe Consumption can surface patterns where session handling does not align with authentication state changes. Even without storing sensitive data in responses, the presence of an unauthenticated API with predictable session identifiers can allow an unauthenticated LLM endpoint exposure to be correlated with session behavior during scans.

For example, a developer might implement Basic Auth like this, inadvertently preserving the session across login:

// Insecure example: session not regenerated after Basic Auth validation
func login(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		user, pass, ok := c.Request().BasicAuth()
		if !ok || !validUserPass(user, pass) {
			return echo.ErrUnauthorized
		}
		// Missing session regeneration; existing session cookie remains
		return next(c)
	}
}

If this handler is used alongside a session middleware that assigns a cookie before login, the session ID remains fixed. An attacker can craft a link that sets a known cookie (e.g., via a malicious site or social engineering), then wait for the victim to authenticate. Because the application does not issue a new session after successful Basic Auth validation, the attacker’s known session becomes the victim’s authenticated session, leading to session fixation.

Additionally, if the API exposes unauthenticated endpoints that return session-related metadata or rely on the same cookie, scans may detect inconsistencies between reported authentication state and session handling. The presence of Basic Auth without secure session rotation increases the risk that an authenticated session can be hijacked or reused beyond its intended scope.

To mitigate session fixation in Echo Go when using Basic Auth, always regenerate the session immediately after successful authentication. Do not rely on the pre‑auth session. Use a secure, server‑side session store, set HttpOnly and Secure flags on cookies, and ensure the session ID is cryptographically random.

Below is a secure implementation that validates Basic Auth and regenerates the session:

import (
	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
	"net/http"
)

func secureLogin(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		user, pass, ok := c.Request().BasicAuth()
		if !ok || !validUserPass(user, pass) {
			return echo.ErrUnauthorized
		}
		// Regenerate session to prevent fixation
		session, err := middleware.GetSession(c)
		if err != nil {
			return echo.NewHTTPError(http.StatusInternalServerError, "failed to get session")
		}
		if err := session.Regenerate(); err != nil {
			return echo.NewHTTPError(http.StatusInternalServerError, "failed to regenerate session")
		}
		// Store minimal, non-sensitive data in session; avoid storing credentials
		session.Values["authenticated"] = true
		session.Values["user"] = user
		// Ensure secure cookie attributes via middleware configuration
		return next(c)
	}
}

// Example secure session middleware setup
func setupSecureSessions(e *echo.Echo) {
	e.Use(middleware.SessionsWithConfig(middleware.SessionConfig{
		CookieName:     "session_id",
		CookiePath:     "/",
		CookieDomain:   "",
		CookieHttpOnly: true,
		CookieSecure:   true,
		CookieSameSite: http.SameSiteStrictMode,
		Expiration:     30 * time.Minute,
		Storage:        middleware.NewMemoryStore(), // or a persistent store in production
	}))
}

In this example, session.Regenerate() creates a new session identifier after successful Basic Auth validation, breaking any linkage to a pre‑set cookie. The cookie attributes HttpOnly, Secure, and SameSite further reduce the risk of theft via XSS or network sniffing. MiddleBrick’s scans can verify that session regeneration occurs on authenticated routes and flag endpoints where cookies lack secure flags.

Additionally, avoid storing sensitive data such as passwords in the session. The remediation guidance from MiddleBrick’s findings would emphasize rotating session identifiers post‑auth, enforcing strict cookie policies, and ensuring that no unauthenticated endpoints expose session identifiers that could be leveraged for fixation.