Software Engineering Institute

The Cisco IOS includes support for the UNIX Line Printer Daemon (LPD) protocol. The LPD service listens on 515/tcp and is not enabled by default.

The IOS LPD service does not properly check the length of the hostname of the router. This error may result in a buffer overflow. See Cisco Security Response Document ID: 99109 for more information about this vulnerability.

From Information Risk Management Advisory 024:
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.

An attacker may be able to execute arbitrary code or create a denial-of-service condition .

Cisco has released an update to address this issue. See Cisco Security Response: Cisco IOS Line Printer Daemon (LPD) Protocol Stack Overflow Document ID: 99109 for more details.

The following workarounds may mitigate this vulnerability.

Restrict access
Using access control lists or firewall rules to limit access to port 515/tcp will prevent attackers from connecting to the LPD service.

Disable the LPD service
Disabling the LPD service will mitigate this vulnerability. See Cisco Security Response Document ID: 99109 for more information.

Disable unencrypted SNMP
The Simple Network Management Protocol (SNMP) service can be used to change settings or monitor device status. Some versions of Cisco IOS support SNMPv1, SNMPv2c, and SNMPv3. To use SNMP commands to change the hostname of an affected device, an attacker would need to know the SNMP read-write community string. SNMPv3 offers authentication and encryption features that may prevent an attacker from obtaining the read-write community string by sniffing Ethernet segments.

Disable SNMP
Disabling SNMP on affected devices may prevent this vulnerability from being exploited.