Request Smuggling in Echo Go with Basic Auth

Request smuggling arises when an HTTP server and a backend service interpret message boundaries differently, allowing an attacker to smuggle a crafted request across security boundaries. In Echo Go, this can occur when the framework parses requests in a way that does not strictly enforce a single, canonical interpretation of ambiguous or malformed HTTP messages. When Basic Auth is used, the presence of an Authorization header can affect routing, access control, or logging, but it does not inherently prevent smuggling if request parsing is inconsistent between the frontend (e.g., a reverse proxy) and Echo Go.

Specifically, an attacker can send requests that combine a valid-looking Authorization header with ambiguous Transfer-Encoding and Content-Length values. For example, a request may include both headers in a way that causes Echo Go to read the body differently than the upstream proxy. If Echo Go trusts the Content-Length while the proxy uses Transfer-Encoding (or vice versa), a smuggled request can reach the backend or another tenant’s route, bypassing intended access controls. Because Basic Auth credentials are often used to enforce per-user or per-client authorization, smuggling can allow an attacker to reuse or manipulate those credentials in downstream requests, escalating impact across authenticated paths.

This risk is not unique to Echo Go but is exposed when the server processes requests with Basic Auth in environments where frontends and backends have differing parsing rules. The smuggled request may not carry the expected Authorization header at the point where Echo Go applies route-level auth checks, allowing unauthorized actions that appear authenticated. Since middleBrick tests unauthenticated attack surfaces, it can detect signs of inconsistent request parsing and missing boundary enforcement, which are precursors to request smuggling in setups that combine frameworks like Echo Go with Basic Auth and shared infrastructure.

To reduce request smuggling risk when using Basic Auth in Echo Go, ensure strict and consistent request parsing on both the frontend and the Echo server. Avoid relying on ambiguous header combinations, and enforce a single body-reading strategy. Below are concrete remediation steps and code examples.

1. Reject requests with both Transfer-Encoding and Content-Length

Drop requests that include both headers, as this is a common smuggling pattern. Implement a request validation middleware in Echo Go.

package main

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

func rejectDualHeaders(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        te := c.Request().TransferEncoding
        cl := c.Request().ContentLength
        if len(te) > 0 && cl >= 0 {
            return echo.NewHTTPError(http.StatusBadRequest, "invalid headers: transfer-encoding and content-length must not both be set")
        }
        return next(c)
    }
}

func main() {
    e := echo.New()
    e.Use(rejectDualHeaders)
    e.GET("/secure", func(c echo.Context) error {
        user, pass, ok := c.Request().BasicAuth()
        if !ok || !validate(user, pass) {
            return echo.ErrUnauthorized
        }
        return c.String(http.StatusOK, "authenticated")
    })
    e.Start(":8080")
}

2. Enforce Content-Length and disable chunked ambiguity

Prefer Content-Length for known-size bodies and avoid relying on Transfer-Encoding: chunked in environments where proxy parsing differs. Configure Echo Go to reject chunked encodings if your deployment topology makes them risky.

package main

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

func limitReadBody(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        // Read and limit body to a safe size using Content-Length
        max := int64(1048576) // 1 MiB
        c.Request().ContentLength = max
        body, err := io.ReadAll(c.Request().Body)
        if err != nil {
            return echo.NewHTTPError(http.StatusBadRequest, "failed to read body")
        }
        if int64(len(body)) > max {
            return echo.NewHTTPError(http.StatusRequestEntityTooLarge, "body too large")
        }
        // Restore body for downstream handlers
        c.Request().Body = io.NopCloser(io.MultiReader(io.NewSectionReader(io.NewReader(body), 0, int64(len(body)))))  
        return next(c)
    }
}

func main() {
    e := echo.New()
    e.Use(limitReadBody)
    e.POST("/data", func(c echo.Context) error {
        user, pass, ok := c.Request().BasicAuth()
        if !ok {
            return echo.ErrUnauthorized
        }
        // process data
        return c.NoContent(http.StatusNoContent)
    })
    e.Start(":8080")
}

3. Normalize Authorization header handling

Ensure the Authorization header is preserved and validated consistently before routing. Do not strip or modify it based on heuristics that may differ between proxy and application.

package main

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

func authMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        user, pass, ok := c.Request().BasicAuth()
        if !ok {
            return echo.ErrUnauthorized
        }
        if !validate(user, pass) {
            return echo.ErrUnauthorized
        }
        // Explicitly set a canonical header to avoid downstream ambiguity
        c.Request().Header.Set("X-Authenticated-User", user)
        return next(c)
    }
}

func validate(user, pass string) bool {
    // Replace with secure credential verification
    return user == "alice" && pass == "correcthorsebatterystaple"
}

func main() {
    e := echo.New()
    e.Use(authMiddleware)
    e.GET("/profile", func(c echo.Context) error {
        return c.String(http.StatusOK, "profile for "+c.Request().Header.Get("X-Authenticated-User"))
    })
    e.Start(":8080")
}

4. Align frontend and backend parsing

Coordinate with your reverse proxy or load balancer to use a single, strict parsing mode. If the frontend strips or transforms headers, ensure Echo Go is configured to expect the same format and not to re-interpret message boundaries.

These steps reduce the conditions that enable request smuggling when Basic Auth is in use. They do not replace broader secure coding practices but specifically address header and body parsing ambiguities that can be exploited in this setup.