1. ASMAX 804 gu router is a SOHO class device. It provides ADSL / WiFi / Ethernet interfaces.

2. There is an *unauthenticated* maintenance script (named 'script') in /cgi-bin/ directory of the web management interface.

3. When 'system' paramether is passed to the script it allows running OS shell commands (as root).

4. PoC:
GET request to:
http://192.168.1.1/cgi-bin/script?system%20whoami

Returns:
root

5. Using CSRF attack one could remotely own a router using for example simple <img> html tags pointing to http://192.168.1.1/...

6. The issue was tested on firmware: 66.34.1

7. The vendor was notified on 30.12.08, but we got no reasonable response till now (the bug remains unpatched).

8. More information: http://www.securitum.pl/dh/asmax-ar-804-gu-compromise