Some Linksys Routers are vulnerable to OS Command injection. You will need credentials to the web interface to access the vulnerable part of the application. Default credentials are always a good starting point. admin/admin or admin and blank password could be a first try. Note: This is a blind OS command injection vulnerability. This means that you will not see any output of your command. Try a ping command to your local system and observe the packets with tcpdump (or equivalent) for a first test. Hint: To get a remote shell you could upload a netcat binary and exec it. WARNING: this module will overwrite network and DHCP configuration.
To display the available options, load the module within the Metasploit console and run the commands 'show options' or 'show advanced':
msf > use auxiliary/admin/http/linksys_wrt54gl_exec
msf auxiliary(linksys_wrt54gl_exec) > show actions
...actions...
msf auxiliary(linksys_wrt54gl_exec) > set ACTION < action-name >
msf auxiliary(linksys_wrt54gl_exec) > show options
...show and set options...
msf auxiliary(linksys_wrt54gl_exec) > run
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