Open Redirect in Echo Go with Mongodb

An open redirect in an Echo Go service that uses MongoDB for user or configuration data occurs when a URL value stored in MongoDB is used to redirect an HTTP response without strict validation. For example, a user profile document in MongoDB may store a preferred return URL after login. If the application retrieves that URL and issues Redirect without verifying the host, an attacker who can write a malicious URL into MongoDB can cause victims to be redirected to arbitrary sites.

In this stack, the chain is: compromised or malicious user input reaches MongoDB (e.g., a profile update stores redirect_url: "https://evil.example.com"), and later an Echo Go handler reads that value and performs an unvalidated redirect. Because MongoDB is the persistence layer, the malicious URL can persist across sessions, making the phishing surface durable. The unauthenticated scan capability of middleBrick can detect endpoints that accept a redirect target parameter and then perform a location-based test, while the OpenAPI/Swagger analysis (with full $ref resolution) can highlight routes that accept a URL without sufficient constraints, cross-referencing runtime behavior where a redirect location is returned in responses.

The risk is not the database itself but the trust placed in stored URLs. Without validating that the redirect target is relative or limited to an allowed host list, an attacker can chain this with social engineering to bypass user trust. This pattern maps to OWASP API Top 10 A05:2023 (Security Misconfiguration) and A03:2023 (Injection), as untrusted data from MongoDB flows directly into an unsafe redirect operation.

To remediate, validate and constrain redirect URLs retrieved from MongoDB in Echo Go. Prefer relative paths for internal redirects, and for external destinations maintain an allowlist of permitted domains. Below is a concrete example of safe handling using MongoDB with Go and Echo.

// models/user.go
package models
type UserProfile struct {
    ID           primitive.ObjectID `bson:"_id"`
    Username     string             `bson:"username"`
    RedirectURL  string             `bson:"redirect_url"`
}

// handlers/user.go
package handlers
import (
    "context"
    "net/http"
    "strings"

    "github.com/labstack/echo/v4"
    "go.mongodb.org/mongo-driver/bson"
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
    "yourproject/models"
)

// safeRedirectURL checks that a stored URL is either relative or matches allowed hosts.
func safeRedirectURL(raw string, allowedHosts map[string]bool) (string, bool) {
    if raw == "" {
        return "", false
    }
    // Reject common redirect bypass patterns
    if strings.HasPrefix(raw, "//") || strings.HasPrefix(raw, "javascript:") {
        return "", false
    }
    // Allow relative paths
    if strings.HasPrefix(raw, "/") {
        return raw, true
    }
    // Validate host against allowlist
    // In practice, parse with url.Parse and compare host/hostname
    // Simplified check for example purposes:
    if allowedHosts["trusted.example.com"] && strings.HasPrefix(raw, "https://trusted.example.com") {
        return raw, true
    }
    return "", false
}

// GetProfile retrieves profile from MongoDB and enforces safe redirect.
func GetProfile(c echo.Context) error {
    client, _ := mongo.Connect(context.TODO(), options.Client().ApplyURI("mongodb://localhost:27017"))
    coll := client.Database("app").Collection("profiles")

    username := c.Param("username")
    var profile models.UserProfile
    err := coll.FindOne(context.TODO(), bson.D{{"username", username}}).Decode(&profile)
    if err != nil {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "not found"})
    }

    allowedHosts := map[string]bool{"trusted.example.com": true}
    redirectTarget, ok := safeRedirectURL(profile.RedirectURL, allowedHosts)
    if !ok {
        redirectTarget = "/dashboard" // safe default
    }
    return c.Redirect(http.StatusFound, redirectTarget)
}

// UpdateProfile accepts user-supplied redirect_url, sanitizes, and stores in MongoDB.
func UpdateProfile(c echo.Context) error {
    var input struct {
        RedirectURL string `json:"redirect_url"`
    }
    if err := c.Bind(&input); err != nil {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid body"})
    }

    allowedHosts := map[string]bool{"trusted.example.com": true}
    safeURL, ok := safeRedirectURL(input.RedirectURL, allowedHosts)
    if !ok {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid redirect_url"})
    }

    client, _ := mongo.Connect(context.TODO(), options.Client().ApplyURI("mongodb://localhost:27017"))
    coll := client.Database("app").Collection("profiles")
    _, err := coll.UpdateOne(context.TODO(), bson.D{{"username", c.Param("username")}}, bson.D{
        {"$set", bson.D{{"redirect_url", safeURL}}},
    })
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "update failed"})
    }
    return c.NoContent(http.StatusOK)
}

Key remediation points specific to MongoDB and Echo Go:

• Never trust stored URLs: treat any redirect_url field in MongoDB as untrusted input.
• Use a strict allowlist for external hosts; prefer relative URLs for internal flows.
• Sanitize on write (UpdateProfile) and re-validate on read (GetProfile) because data may originate from multiple clients or legacy entries.
• Reject //-protocol-relative URLs and javascript: schemes to prevent protocol bypass and script execution.
• Log validation failures for audit; do not expose raw redirect values in error messages to avoid information leakage.

By combining MongoDB input constraints with Echo Go’s handler discipline, you ensure that even if a malicious URL enters the database, it cannot be used to abuse the redirect flow. This approach aligns with secure coding practices and reduces the attack surface for open redirect vulnerabilities in this technology stack.