New vulnerability has been discovered in the open source Internet Systems Consortium DHCP server. This vulnerability allows a remote attacker to execute a malicious code on victim’s computer.

All versions prior to 3.1-ESV-R1, 4.1-ESV-R2 and 4.2.1-P1 are affected by this bug as they do not strip or escape certain shell meta-characters in responses from the dhcp server (like hostname) before passing the responses on to dhclient-script. Depending on the script and OS, this can result in execution of exploit code on the client.

ISC recommends users to upgrade their system and as a workaround to disable hostname update by setting DHCLIENT_SET_HOSTNAME=”no” in /etc/sysconfig/network/dhcp on SUSE.

Other systems may add following line to dhclient-script at the beginning of the set_hostname() function:

new_host_name=${new_host_name//[^-.a-zA-Z0-9]/}

In environments where filters/acls can be put into place to limit clients to accessing only legitimate dhcp servers, this will protect clients

from rogue dhcp servers deliberately trying to exploit this bug. However, this will not protect from compromised servers.

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