ApostropheCMS: publicApiProjection Bypass via project Query Builder in Piece-Type REST API

## Summary 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`: ```javascript // 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: ```javascript // 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: ```javascript // 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: ```javascript // 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: ```bash 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: ```bash 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: ```bash 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. ## Impact - **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. ## Recommended Fix 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: ```javascript // 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 }); } } ```

Source published

16 Apr 2026 20:42:21 UTC

Source modified

16 Apr 2026 21:11:29 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Publisher rating · MODERATE