CVE 2011-3872
Puppet 2.6.x before 2.6.12 and 2.7.x before 2.7.6, and Puppet Enterprise (PE) Users 1.0, 1.1, and 1.2 before 1.2.4, when signing an agent certificate, adds the Puppet master's certdnsnames values to the X.509 Subject Alternative Name field of the certificate, which allows remote attackers to spoof a Puppet master via a man-in-the-middle (MITM) attack against an agent that uses an alternate DNS name for the master, aka "AltNames Vulnerability."
See the 
CVE page on Mitre.org
for more details.
