The ISC Dynamic Host Configuration Protocol (DHCP) client, dhclient, in versions 3.0.x through 4.2.x before 4.2.1-P1, 3.1-ESV before 3.1-ESV-R1, and 4.1-ESV before 4.1-ESV-R2 allows remote attackers to execute arbitrary commands by way of shell metacharacters in a hostname obtained from a DHCP message, as demonstrated by a hostname that is provided to dhclient-script.
Impact
The dhclient process allows hostile DHCP servers to execute arbitrary commands by way of shell metacharacters.