D-Link Captcha Bypass
D-Link released new firmware designed to protect against malware that alters DNS settings by logging in to the router using default administrative credentials. There is a flaw in the captcha authentication system that allows an attacker to glean your WiFi WPA pass phrase from the router with only user-level access, and without properly solving the captcha. When you login with the captcha enabled, the request looks like this: GET /post_login.xml?hash=c85d324a36fbb6bc88e43ba8d88b10486c9a286a&auth_code=0C52F&auth_id=268D2. The hash is a salted MD5 hash of your password, the auth_code is the captcha value that you entered, and the auth_id is unique to the captcha image that you viewed (this presumably allows the router to check the auth_code against the proper captcha image). The problem is that if you leave off the auth_code and auth_id values, some pages in the D-Link Web interface think that you’ve properly authenticated, as long as you get the hash right: GET /post_login.xml?hash=c85d324a36fbb6bc88e43ba8d88b10486c9a286a. Most notably, once you’ve made the request to post_login.xml, you can activate WPS with the following request: GET /wifisc_add_sta.xml?method=pbutton&wps_ap_ix=0. When WPS is activated, anyone within WiFi range can claim to be a valid WPS client and retrieve the WPA passphrase directly from the router.
