Vulnerability Note VU#284857

There are multiple remote buffer overflow vulnerabilities in the ISC implementation of DHCP. As described in RFC 2131, "the Dynamic Host Configuration Protocol (DHCP) provides a framework for passing configuration information to hosts on a TCP/IP network." In addition to supplying hosts with network configuration data, ISC DHCPD allows the DHCP server to dynamically update a DNS server, obviating the need for manual updates to the name server configuration. Support for dynamic DNS updates is provided by the NSUPDATE feature.

During an internal source code audit, developers from the ISC discovered several vulnerabilities in the error handling routines of the minires library, which is used by NSUPDATE to resolve hostnames. These vulnerabilities are stack-based buffer overflows that may be exploitable by sending a DHCP message containing a large hostname value. Note: Although the minires library is derived from the BIND 8 resolver library, these vulnerabilities do not affect any current versions of BIND.

Remote attackers may be able to execute arbitrary code with the privileges of the user running ISC DHCPD.

Upgrade or apply a patch

The ISC has addressed these vulnerabilities in versions 3.0pl2 and 3.0.1RC11 of ISC DHCPD. If your software vendor supplies ISC DHCPD as part of an operating system distribution, please see the vendor section of this document.

Disable dynamic DNS updates (NSUPDATE)

As an interim measure, the ISC recommends disabling the NSUPDATE feature on affected DHCP servers.

Block external access to DHCP server ports

As an interim measure, it is possible to limit exposure to these vulnerabilities by restricting external access to affected DHCP servers on the following ports:

bootps      67/tcp      # Bootstrap Protocol Server
bootps      67/udp      # Bootstrap Protocol Server
bootpc      68/tcp      # Bootstrap Protocol Client
bootpc      68/udp      # Bootstrap Protocol Client