Insecure Direct Object Reference in Chi with Mongodb

Insecure Direct Object Reference (IDOR) occurs when an API exposes internal object references, such as database IDs, in requests without adequate authorization checks. In a Chi-based service written in Go, this commonly arises when route parameters like userID or documentID are taken directly from the request and used to construct a MongoDB query without verifying that the authenticated subject has permission to access that specific object.

Chi provides a minimal, idiomatic router and middleware toolkit. When handlers extract parameters via chi.URLParam(r, "id") and plug them straight into a MongoDB Go driver query, the application implicitly trusts the client-supplied identifier. For example, consider a route pattern /users/{userID}/profile. If the handler does not confirm that the authenticated user is allowed to view the profile for the supplied userID, an attacker can change the URL to access another user’s profile simply by modifying the path parameter.

With MongoDB, the risk is compounded by how queries are built. Suppose the handler constructs a filter like bson.M{"_id": userID} where userID comes directly from the URL. There is no ownership or role-based check tying the authenticated subject to that _id. An attacker can enumerate valid ObjectIDs or guess predictable values and retrieve records they should not see. This becomes particularly dangerous when sensitive fields such as email, PII, or internal references are returned in the document. The combination of Chi’s straightforward routing and MongoDB’s flexible document structure makes it easy to inadvertently expose object-level access control if authorization is not explicit at the data-access layer.

Another common pattern is using a URL parameter to reference a related subdocument, such as /orgs/{orgID}/members/{memberID}. If the handler queries MongoDB with something like bson.M{"orgID": orgID, "memberID": memberID} without validating that the requester belongs to orgID, the request becomes vulnerable. Because MongoDB does not enforce application-level permissions, the onus is on the service to implement checks. Without such checks, the API returns data based solely on user-supplied identifiers, which is the essence of an IDOR condition in a Chi + MongoDB stack.

Real-world attack patterns mirror findings in the OWASP API Top 10 and map to IDOR as a broken access control issue. Unlike authentication flaws, IDOR assumes the attacker is authenticated as a low-privilege account but can manipulate object references to access higher-privilege data. In MongoDB, ObjectIDs are not inherently unguessable, and developers sometimes mistakenly believe that storing data in separate collections provides implicit isolation. Chi routes that do not enforce tenant or ownership boundaries therefore expose a straightforward path for horizontal privilege escalation across records.

To detect such issues, scanners like middleBrick run unauthenticated and authenticated tests that probe endpoints with modified identifiers to see whether authorization is enforced. They check whether responses for altered object references differ appropriately (e.g., 403 or 404) and whether data exposure occurs. Because IDOR is about authorization rather than syntax, the vulnerability resides in the logic that binds user identity to MongoDB query filters, not in the choice of Chi or MongoDB alone.

Remediation focuses on ensuring every MongoDB query is constrained by the authenticated subject’s permissions. In Chi, this typically means enriching the request context with identity and role information and using it to build scoped filters. Below are concrete patterns and code examples that demonstrate how to secure Chi endpoints that interact with MongoDB.

First, always derive the query filter from the authenticated subject rather than from user-supplied identifiers alone. For example, if the endpoint is /profile and the user is authenticated via JWT, the handler should resolve the subject from the token and use it as the primary key in the query:

userID, ok := ctx.UserValue("userID").(string)
if !ok {
    http.Error(w, "unauthorized", http.StatusUnauthorized)
    return
}
var filter bson.M = bson.M{
    "_id": userID,
    // additional tenant or ownership fields if applicable
}
err := coll.FindOne(ctx, filter).Decode(&result)

This ensures that even if the request contains a different identifier, the database lookup is bound to the authenticated subject. Note that ctx.UserValue would be populated by an earlier authentication middleware that validates tokens and injects claims into Chi’s context.

For endpoints that accept an identifier but must still enforce ownership, combine the supplied identifier with the subject’s ID:

suppliedID := chi.URLParam(r, "documentID")
userID, _ := ctx.UserValue("userID").(string)
var filter bson.M = bson.M{
    "_id": suppliedID,
    "ownerID": userID,
}
var doc Document
err := coll.FindOne(ctx, filter).Decode(&doc)
if err != nil {
    http.Error(w, "not found", http.StatusNotFound)
    return
}

This pattern prevents horizontal IDOR by requiring that the document both matches the supplied ID and belongs to the requesting user. It is especially important when ObjectIDs are predictable or when references are shared across users.

For organization-based access, embed the tenant or organization ID in the document schema and scope queries accordingly:

orgID := chi.URLParam(r, "orgID")
userOrgID, _ := ctx.UserValue("orgID").(string)
if orgID != userOrgID {
    http.Error(w, "forbidden", http.StatusForbidden)
    return
}
var filter bson.M = bson.M{
    "orgID": orgID,
    "members.memberID": chi.URLParam(r, "memberID"),
}

Using the MongoDB Go driver, prefer parameterized queries and avoid string concatenation to prevent injection. Also ensure that indexes on fields like ownerID and orgID exist to maintain performance while enforcing these filters.

Finally, apply the principle of least privilege to the MongoDB connection used by the Chi service. Use a database user with read/write rights only on the necessary collections and avoid broad administrative credentials. Together, these measures close the IDOR vector while keeping the Chi routing layer clean and explicit.