Path Traversal in Echo Go with Mongodb

Path Traversal occurs when user-controlled input is used to construct file or database paths without proper validation, allowing an attacker to access arbitrary resources. In an Echo Go application that uses Mongodb, this typically arises when a request parameter (such as filename or document_id) is directly interpolated into a Mongodb query or filesystem path. Because Echo Go does not sanitize path segments, an attacker can supply sequences like ../../../etc/passwd or crafted ObjectId values to traverse logical boundaries.

With Mongodb, traversal risks often map to Insecure Direct Object References (IDOR) and BOLA (Broken Object Level Authorization) checks. If an endpoint accepts a user-supplied ID and uses it in a Mongodb filter (e.g., bson.M{"_id": userInput}) without verifying ownership or context, an attacker may read or modify documents they should not access. For example, an ID like 507f1f77bcf86cd799439011 may be valid, but an attacker can try adjacent or known ObjectIds to enumerate records. Similarly, if the application builds filesystem paths for attachments stored on disk and uses Mongodb to store those paths, unsanitized input can escape intended directories when combined with path concatenation, leading to unauthorized file reads or writes.

Another specific scenario involves storing file paths in Mongodb documents and later using user input to select which path to retrieve. If the application trusts the stored path and appends user input without cleaning, the combined path may traverse outside the intended directory tree. This becomes critical when the Echo Go route uses parameters like :file and directly passes them to a function that builds a Mongodb query or a filesystem path. The scanner checks described in the middleBrick LLM/AI Security and Property Authorization categories can detect missing authorization logic around these endpoints, flagging BOLA/IDOR and Unsafe Consumption findings that indicate path traversal exposure.

Real-world attack patterns mirror standard OWASP API Top 10 #1 Broken Object Level Authorization and #5 Broken Function Level Authorization. For instance, an attacker might send a request like GET /files/../../../secret.txt to an Echo Go route that resolves the path and queries Mongodb for associated metadata. Even when ObjectId parameters are used, an attacker can probe valid ObjectId patterns to access other documents. middleBrick’s active prompt injection and system prompt leakage checks are designed to surface LLM-related exposures, but for traditional API endpoints, the presence of unvalidated paths and IDs is detected through BOLA/IDOR and Property Authorization scans, which highlight missing ownership checks and excessive data exposure.

To reduce risk, developers should treat all user input as untrusted, apply strict allowlists on path components, and enforce authorization checks before querying Mongodb. Using parameterized queries and avoiding direct string concatenation for paths and filters is essential. middleBrick’s scanning flow tests the unauthenticated attack surface and can surface these classes of issues, providing prioritized findings with remediation guidance mapped to compliance frameworks such as OWASP API Top 10 and SOC2.

Remediation focuses on input validation, canonicalization, and strict authorization before any Mongodb operation. In Echo Go, use context-aware validation for route parameters and bind inputs to structured types instead of raw strings. For ObjectId handling, rely on the official MongoDB Go driver’s ObjectId parsing, which rejects malformed IDs and prevents injection via malformed hex strings.

Example: Safe ObjectId retrieval with ownership check

import (
    "context"
    "github.com/labstack/echo/v4"
    "go.mongodb.org/mongo-driver/bson"
    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
    "go.mongodb.org/mongo-driver/bson/primitive"
)

type DocumentService struct {
    collection *mongo.Collection
}

func (s *DocumentService) GetDocument(c echo.Context) error {
    userID := c.Get("userID").(string) // from auth middleware
    idParam := c.Param("id")
    objID, err := primitive.ObjectIDFromHex(idParam)
    if err != nil {
        return echo.NewHTTPError(400, "invalid document id")
    }

    // Enforce BOLA: ensure the document belongs to the requesting user
    var doc Document
    err = s.collection.FindOne(c.Request().Context(), bson.M{
        "_id": objID,
        "owner_id": userID,
    }).Decode(&doc)
    if err == mongo.ErrNoDocuments {
        return echo.NewHTTPError(404, "document not found")
    }
    if err != nil {
        return echo.NewHTTPError(500, "database error")
    }
    return c.JSON(200, doc)
}

This example demonstrates strict input validation via primitive.ObjectIDFromHex, which returns an error for malformed IDs, preventing injection through malformed hex characters. The query includes an explicit owner_id filter, enforcing BOLA so users cannot read or modify others’ documents via guessed or traversed IDs.

Example: Safe filesystem path resolution

import (
    "path"
    "strings"
)

func sanitizePath(userInput string) (string, error) {
    // Reject path traversal sequences
    if strings.Contains(userInput, "..") {
        return "", echo.NewHTTPError(400, "invalid path")
    }
    // Clean and restrict to a base directory
    cleaned := path.Clean("/safe/base" + "/" + userInput)
    if !strings.HasPrefix(cleaned, "/safe/base") {
        return "", echo.NewHTTPError(400, "path traversal detected")
    }
    return cleaned, nil
}

The sanitizePath function rejects inputs containing .. and uses path.Clean to collapse separators, then verifies the cleaned path remains within the allowed base directory. This approach prevents traversal when constructing paths that may later be stored or queried in Mongodb fields.

General remediation practices

• Use allowlists for filenames and identifiers; reject any characters not explicitly permitted.
• Always enforce ownership checks at the database query level (BOLA mitigation).
• Avoid storing and later using raw user input in filesystem paths; prefer storing stable keys and mapping to paths server-side.
• Leverage the MongoDB Go driver’s built-in validation for ObjectId and timestamps to avoid injection via malformed inputs.

These steps align with the Property Authorization and Input Validation checks that middleBrick scans perform. By combining strict validation, parameterized queries, and explicit authorization, you reduce the attack surface presented by path traversal in Echo Go applications using Mongodb.