In this level, we are presented with a login dialog with the title "CISCO IDS WEB LOGIN SYSTEM".
If we search Google for "Cisco IDS default password", the first hit summary mentions a default username of netrangr and root, and a default password of attack. Google is nice enough to show this in the page summary, too, so we don't even have to click through. (see: http://www.cisco.com/c/en/us/support/docs/security/ips-4200-series-sensors/13837-34.html)
If we enter root in the username field and attack, we get a popup that says: ssaptluafed_sigalf_cesofni, which if we reverse gives us our flag.
Also, as mentioned in the Bonus section in the top level write-up, you can use level15 to solve this level by viewing the source code of the page.
infosec_flagis_defaultpass