Prototype Pollution in Echo Go with Basic Auth

Prototype pollution in Go handlers using the Echo framework can occur when user-controlled input modifies the prototype of shared objects, such as map[string]interface{} used across requests. When Basic Authentication is enforced via middleware, the focus often shifts to credential validation, which can inadvertently obscure how request bodies, query parameters, or headers are merged into application state. An attacker may supply crafted keys such as __proto__, constructor, or prototype in JSON payloads or form values. If the application performs shallow merges into a global or package-level configuration object, these keys can change behavior for subsequent requests, including authentication checks performed by Basic Auth middleware.

Consider a scenario where Echo routes use a shared preferences map updated from request parameters without sanitization:

var sharedConfig = map[string]interface{}{
    "rateLimit": 100,
}

func updateConfig(c echo.Context) error {
    raw := make(map[string]interface{})
    if err := c.Bind(&raw); err != nil {
        return err
    }
    for k, v := range raw {
        sharedConfig[k] = v
    }
    return c.JSON(map[string]string{"status": "ok"})
}

An authenticated request (Basic Auth) with body {"__proto__": {"isAdmin": true}} can pollute sharedConfig so that isAdmin appears on all maps, potentially bypassing authorization checks elsewhere. The Basic Auth middleware may have already validated credentials, but the polluted configuration can change how later handlers interpret roles or permissions. Because Echo does not sanitize keys by default, the merge becomes an injection vector on the application object model.

In the context of middleBrick scanning, this pattern would be flagged under BOLA/IDOR and Input Validation checks, with remediation guidance to avoid global mutation and to validate/sanitize keys. The scan does not modify code; it highlights how an authenticated endpoint can still expose logic flaws when input handling is permissive.

To secure Basic Auth in Echo while preventing prototype pollution, avoid mutating shared objects and explicitly permit known keys. Validate credentials using a dedicated function and isolate authentication state from request-bound configuration. Below is a hardened example that parses credentials safely and rejects polluted keys.

First, define a structured configuration type and a whitelist of allowed keys for runtime updates:

type AppConfig struct {
    RateLimit int `json:"rateLimit"`
    LogLevel  string `json:"logLevel"`
}

var config = AppConfig{
    RateLimit: 100,
    LogLevel:  "info",
}

var allowedKeys = map[string]bool{
    "rateLimit": true,
    "logLevel":  true,
}

Next, implement Basic Auth middleware using echo.BasicAuth with a validator that checks credentials against a secure source. Do not rely on request body data for auth decisions:

func secureBasicAuth(next echo.HandlerFunc) echo.HandlerFunc {
    return echo.BasicAuth(func(username, password string) (bool, error) {
        // In production, use constant-time comparisons and a secure store
        validUser := username == "admin" && password == "s3curePass!"
        return validUser, nil
    })
}

Then, create a dedicated update endpoint that binds to a controlled DTO and only applies whitelisted fields:

func updateConfigSafe(c echo.Context) error {
    var dto struct {
        RateLimit *int  `json:"rateLimit"`
        LogLevel  *string `json:"logLevel"`
    }
    if err := c.Bind(&dto); err != nil {
        return c.JSON(400, map[string]string{"error": "invalid payload"})
    }

    // Apply only known fields
    if dto.RateLimit != nil && allowedKeys["rateLimit"] {
        config.RateLimit = *dto.RateLimit
    }
    if dto.LogLevel != nil && allowedKeys["logLevel"] {
        config.LogLevel = *dto.LogLevel
    }

    return c.JSON(config)
}

Finally, register routes with the auth middleware applied to protected paths:

e := echo.New()

// Public endpoint
 e.GET("/health", func(c echo.Context) error {
    return c.String(200, "ok")
 })

// Protected endpoint
 e.POST("/config", secureBasicAuth(updateConfigSafe))

 e.Logger.Fatal(e.Start(":8080"))

This approach ensures that Basic Auth validates identity without exposing configuration to mutation, mitigating prototype pollution risks. middleBrick’s scans can verify that such patterns are in place by testing input handling and auth separation.