[Full-disclosure] linksys WRT54g authentication bypass

Type securityvulns
Reporter Securityvulns
Modified 2006-08-04T00:00:00


I'm having some trouble believing this hasn't been reported before. If you have a linksys router handy, please check to see whether it is vulnerable to this attack. It's possible that all of the linksys router web UIs have the same bug. Hopefully the problem is isolated to one particular model or firmware revision.


Tested product: Linksys WRT54g home router, firmware revision 1.00.9.

Problem #1: No password validation for configuration settings.

The WRT54g does not attempt to verify a username and password when configuration settings are being changed. If you wish to read configuration settings, you must provide the administrator ID and password via HTTP basic authentication. No similar check is done for configuration changes.

This request results in a user-id and password prompt: GET /wireless.htm

This request disables wireless security on the router, with no password prompt: POST /Security.tri Content-Length: 24


Problem #2: Cross-site request forgery

The web administration console does not verify that the request to change the router configuration is being made with the consent of the administrator. Any web site can force a browser to send a request to the linksys router, and the router will accept the request.

II. Exploitation

The combination of these two bugs means that any internet web site can change the configuration of your router. Recently published techniques for port-scanning and web server finger printing via java and javascript make this even easier. The attack scenario is as follows:

  • intranet user visits a malicious web site
  • malicious web site returns specially crafted HTML page
  • intranet user's browser automatically sends a request to the router that enables the remote administration interface
  • the owner of the malicious web site now has complete access to your router

I'm not going to share the "specially crafted HTML page" at this time, but it isn't all that special.


If your router is vulnerable, the following curl command will disable wireless security on your router. Tests for other router models and firmware revisions may be different:

curl -d "SecurityMode=0&layout=en"


1) Make sure you've disabled the remote administration feature of your router. If you have this "feature" enabled, anybody on the internet can take control of the router.

2) Change the IP address of the router to a random value, preferably in the range assigned to private networks. For example, change the IP address to 10.x.y.z, where x, y, and z are numbers between 0 and 255 inclusive. This makes it more difficult for an attacker to forge the request necessary to change the router configuration. This mitigation technique might not help much if you have a java-enabled browser, because of recently published techniques for determining gateway addresses via java applets.

3) Disable HTTP access to the administration interface of the router, allowing only HTTPS access. Under most circumstances, this will cause the browser to show a certificate warning before the configuration is changed.


Linksys customer support was notified on June 24, 2006. Full disclosure on August 4, 2006.

-- GR

Is your PC infected? Get a FREE online computer virus scan from McAfee® Security. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963

Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/