Identification Failures in Chi with Mongodb

Identification failures occur when an application cannot reliably establish and maintain the identity of a subject across interactions. In Chi, a functional programming web framework for Clojure, this typically manifests as insufficient binding of authenticated identity to downstream data access layers. When paired with MongoDB, an identification failure becomes more dangerous because queries and updates often rely on developer-supplied filters that may omit or misinterpret identity constraints.

Chi routes are typically composed as a series of middleware and handlers. If identity is stored in a request map (e.g., under :identity or ) but a handler constructs MongoDB queries without explicitly validating or merging that identity into the filter, an attacker can manipulate parameters to access records belonging to other subjects. For example, a handler that builds a query like {"userId" userId} where userId is derived from a token but not re-verified against the request map is vulnerable to IDOR-like behavior.

Another common pattern in Chi applications is the use of path parameters or query strings to reference resources without confirming that the authenticated subject owns those resources. MongoDB’s flexible schema can inadvertently support this if application logic does not enforce ownership checks at the database level. For instance, a GET route /api/records/:id might retrieve a document by its _id without ensuring the document’s ownerId matches the authenticated user’s ID. This is an Identification Failure because the system fails to guarantee that the requesting subject is the rightful owner or authorized viewer of the targeted data.

In Chi, this often stems from treating the request map as a trusted source of identity without cross-checking it against the data access layer. If middleware injects a user ID based on JWT claims but subsequent handlers do not consistently apply that ID to MongoDB filters, the attack surface expands. Attackers can craft requests with altered path parameters or manipulated query fields to probe whether the system enforces identity-based boundaries. Because MongoDB queries are constructed dynamically in application code, missing or inconsistent identity binding can lead to unauthorized read or write operations across multiple records.

Additionally, Chi’s composability can exacerbate identification failures when handlers are chained. A handler responsible for enriching a request map with user details might be omitted in certain routes, or a developer might forget to propagate the identity into a MongoDB query builder. This inconsistency results in an unauthenticated or under-authenticated data access path, which middleBrick’s Authentication and BOLA/IDOR checks are designed to surface. The scanner evaluates whether endpoints properly bind authentication context to database operations, highlighting routes where identity is not explicitly enforced in MongoDB filters.

Real-world exploitation scenarios include modifying a numeric ID in a URL to access another user’s data or manipulating JSON payloads to omit identity fields that the server should enforce. Because MongoDB does not inherently understand application-level ownership, it is the developer’s responsibility to ensure every query includes a subject-bound filter. Identification failures in Chi with MongoDB therefore center on gaps in binding authenticated identity to database operations, allowing attackers to traverse privilege boundaries through parameter manipulation.

Remediation focuses on ensuring that every MongoDB query in a Chi application explicitly incorporates the authenticated subject’s identity. This requires disciplined handling of the request map and consistent construction of query filters.

First, always derive the user identifier from the request map and merge it into the query filter. Avoid relying on path parameters or client-supplied IDs for ownership checks. Below is an example of a secure Chi handler that binds identity to a MongoDB query using the official MongoDB Clojure driver:

(ns myapp.handlers
  (:require [cheshire.core :as json]
            [monger.core :as mg]
            [monger.collection :as mc]))

(defn get-user-records [request]
  (let [db (:database request)
        user-id (:user-id request) ; bound from authenticated middleware
        filter {"userId" user-id}]
    (mc/find-maps db "records" filter)))

This pattern guarantees that even if an attacker manipulates URL parameters, the query will only return records where the userId field matches the authenticated subject. The :user-id must be set by middleware that validates the token or session and ensures it cannot be overridden by client input.

Second, for endpoints that accept resource identifiers, perform an ownership check before operating on the document. For example, when updating a record, fetch the document first and verify ownership:

(defn update-record [request record-id updates]
  (let [db (:database request)
        user-id (:user-id request)
        record (mc/find-map-by-id db "records" record-id)]
    (if (and record (= (:userId record) user-id))
      (mc/update-by-id db "records" record-id {$set updates})
      {:status 403 :body "Forbidden"})))

This two-step approach — retrieve then validate — prevents IDOR by confirming that the record’s userId matches the authenticated user before applying changes. It also avoids the risk of updating arbitrary documents by injecting user-controlled IDs directly into update operations.

Third, when using aggregation pipelines or more complex queries, embed the user identifier at the pipeline entry point. For instance, to list accessible documents with additional joins:

(defn user-documents [request]
  (let [db (:database request)
        user-id (:user-id request)]
    (mc/aggregate db "records"
                  [{:$match {"userId" user-id}}
                   {$lookup "{:from "users" :localField "ownerId" :foreignField "_id" :as "owner"}}])))

Ensure that the $match stage is constructed programmatically with the authenticated subject’s ID rather than accepting it from external input. This practice extends to any dynamic query building, where filters must be composed server-side with identity as a non-negotiable constraint.

Finally, adopt a middleware layer that enforces identity binding globally. In Chi, you can wrap handlers to inject and validate the user identifier before reaching route-specific logic. This centralizes security logic and reduces the chance of accidental omission in individual handlers.