Flaw in ISC’s dhclient could allow remote code execution

ISC logoThe Internet Systems Consortium (ISC), a non-profit company which develops BIND and dhcpd/dhclient, has announced a new remote code execution vulnerability present in its dhclient software.

If you only administer Windows and Macs you may not need to read on. Those of us with a proclivity for Linux, FreeBSD and other Unix or Unix-like platforms should take notice.

(Windows and OS X users – you can relax because neither operating system uses the ISC’s dhclient software. Even though OS X is BSD-based, it uses an Apple utility called IPConfiguration.bundle as its DHCP client. )

The flaw (known as CVE-2011-0997) described in the advisory can be exploited by a rogue DHCP server, or a server that has been compromised to send out malicious responses.

The problem is in versions before 3.1-ESV-R1, 4.1-ESV-R2 or 4.2.1-P1. Attackers can send DHCP hostname replies to clients that may contain shell code which could be used to exploit the client machine with the privileges of dhclient.

ISC advisory severityISC has published advice on how to mitigate against the exploit, in addition to fixing the bugs in the main distribution. It will likely take some time before all of the different Linux distributions consume the fixes and deploy them to their users.

If you have critical infrastructure in which you use the dhclient software to handle IP addressing, you may wish to take ISC’s mitigation advice. While this attack has not yet been seen in the wild, now that it is known it could be used to gain a foothold in targeted organizations.