The mod_tls module in ProFTPD before 1.3.2b, and 1.3.3 before 1.3.3rc2,
when the dNSNameRequired TLS option is enabled, does not properly handle a
'\0' character in a domain name in the Subject Alternative Name field of an
X.509 client certificate, which allows remote attackers to bypass intended
client-hostname restrictions via a crafted certificate issued by a
legitimate Certification Authority, a related issue to CVE-2009-2408.