Cisco devices running IOS software may be prone to a denial of service attack if a URL containing a question mark followed by a slash (?/) is requested. The device will enter an infinite loop when supplied with a URL containing a "?/" and an enable password. Subsequently, the router will crash in two minutes after the watchdog timer has expired and will then reload. In certain cases, the device will not reload and a restart would be required in order to regain normal functionality.
This vulnerability is restricted to devices that do not have the enable password set or if the password is known or can be easily predicted. The vulnerable service is only on by default in the Cisco 1003, 1004 and 1005 routers.
Users can identify vulnerable or invulnerable devices running IOS by logging onto the device and issuing the ?show version? command. If IOS is running on a vulnerable device the command will return ?Internetwork Operating System Software? or ?IOS (tm)? with a version number.
Vulnerable IOS software may be found on the following Cisco devices:
*Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900, 1000, 1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000, 4500, 4700, AS5200, AS5300, AS5800, 6400, 7000, 7200, ubr7200, 7500, and 12000 series.
*Recent versions of LS1010 ATM switch.
*Catalyst 6000 with IOS.
*Catalyst 2900XL LAN switch with IOS.
Cisco IOS HTTP Server ?/ String Handling Local DoS
Remote / Network Access
Denial of Service,
Loss of Availability
Cisco devices running IOS software may be prone to a denial of service attack if a URL containing the question mark followed by a slash (?/) is requested. The device will enter an infinite loop when the supplied with the URL containing a "?/" and an enable password. Subequently, the router or switch will crash in two minutes after the watchdog timer has expired and will then reload. In certain cases the device will not reload and restart. In such a case, however, a manual restart would be required to regain normal functionality.
Upgrade to the version appropriate for your installation, as outlined in the vulnerable version matrix provided by Cisco. It is also possible to correct the flaw by implementing the following workaround(s): Disable the HTTP server on the IOS device, or apply an access control list to mitigate risk by reducing your exposure.