Advisory 024
Cisco IOS LPD Remote Stack Overflow
Vulnerability Type / Importance: Remote Code Execution / High
Problem Discovered: 30 July 2007
Vendor Contacted: 30 July 2007
Advisory Published: 10 October 2007
Abstract:
The LPD daemon included in Cisco IOS is vulnerable to a remote stack overflow
Description:
The Line Printer Daemon, which provides print server functionality in Cisco IOS is vulnerable to a software flaw whereby the length of the hostname of the router is not checked before being copied into a fixed size memory buffer. This results in IOS crashing if the hostname is too long, but could potentially result is arbitrary code execution. However, the attacker must be able to control the hostname of the router, which could be achieved via SNMP.
Technical Details:
When the LPD daemon is configured in Cisco IOS it listens on the default LPD TCP port, 515. If connected to with a source TCP port of anything other than 515 the following error is displayed:
$ telnet 172.30.3.101 515
Trying 172.30.3.101...
Connected to 172.30.3.101 (172.30.3.101).
Escape character is '^]'.
hostname_of_the_router: /usr/lib/lpd: Malformed from address
If the hostname is 99 characters or longer then the overflow occurs as the result of a call to the sprintf() function. Although this is technically a stack overflow, because IOS allocates heap memory for process stacks, the memory overwritten is actually heap. However, as the heap memory is acting as a stack, the return address, stored before the start of the character buffer, can be overwritten by the hostname when the overflow occurs, but for some reason the crash doesn’t occur until the buffer intrudes into the “red zone” at the boundary of the heap chunk. Therefore, when the crash happens and the router reboots, the memory dump indicates heap corruption.
It must be reiterated that control of the hostname is required to exploit this vulnerability. If SNMP is running on the device and the rw community string is known (this is often set to the default value “private”) then the hostname can be set as follows:
$ snmpset -Os -c private -v 1 10.0.0.1 system.sysName.0 s long_hostname
Vendor & Patch Information:
Cisco have released an update to resolve this issue; this can be downloaded from:
http://www.cisco.com/warp/public/707/cisco-sr-20071010-lpd.shtml
Workaround:
Cisco have provided the following workaround to mitigate this vulnerability:
Tested/Affected Versions:
IRM identified this vulnerability in IOS version 12.3(22)
Credits:
Research & Advisory: Andy Davis
Disclaimer:
All information in this advisory is provided on an 'as is' basis in the hope that it will be useful. Information Risk Management Plc is not responsible for any risks or occurrences caused by the application of this information.