Published: 28 August 2007
sink.c in fetchmail before 6.3.9 allows context-dependent attackers to cause a denial of service (NULL dereference and application crash) by refusing certain warning messages that are sent over SMTP.
From the Ubuntu security team
Earl Chew discovered that fetchmail can be made to de-reference a NULL pointer when contacting SMTP servers. This vulnerability can be used by attackers who control the SMTP server to crash fetchmail and cause a denial of service. (CVE-2007-4565)