Public Vulnerability Reports

Denial of Service Vulnerability in Linksys BEFSR41 EtherFast Cable/DSL Router



Linksys Group Inc.'s EtherFast Cable/DSL Router with 4-Port Switch "is the perfect option to connect multiple PCs to a high-speed Broadband Internet connection or to an Ethernet back-bone. Allowing up to 253 users, the built-in NAT technology acts as a firewall protecting your internal network." More information about it is available at


The BEFSR41 crashes if a remote and/or local attacker accesses the script Gozila.cgi using the router's IP address with no arguments. Remote exploitation requires that the router's remote management be enabled and that the proper password is supplied. A sample request looks as follows:


Because successful exploitation requires password authentication, exploitation can only occur in two likely scenarios:

1.) The Linksys user is socially engineered into clicking on a link and authenticating to the router (e.g. "Check out this cool Linksys Easter Egg! Click here!")

2.) The Linksys user is logged into the router's web management console, and is the vicitm of a cross site scripting attack which redirects the user to this link.


This vulnerability affects the BEFSR41 EtherFast Cable/DSL router with firmware earlier than version 1.42.7.


Pressing the reset button on the back of the router should restore normal functionality.


Firmware version 1.42.7 and later fix this problem. Version 1.43, which is the latest available version, can be found at


The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project has assigned the identification number CAN-2002-1236 to this issue.


08/27/2002 Issue disclosed to iDEFENSE
09/12/2002 Linksys notified
09/12/2002 iDEFENSE clients notified
09/13/2002 Response received from
09/19/2002 Status request from iDEFENSE
09/20/2002 Asked to delay advisory until second level support can respond
10/20/2002 No response from second level support, another status request to
10/31/2002 Still no response from Linksys, public disclosure
11/06/2002 Vendor Response from Andreas Bang, Linksys Product Manage


Jeep 94 ( is credited with discovering this vulnerability.