Sylpheed is a GTK+ based fast email client.
A buffer overflow bug has been found in the way Sylpheed handles non-ASCII characters in the header of a message to which a victim replies. A carefully crafted email message could potentially allow an attacker to execute arbitrary code on a victim's machine if they reply to such a message. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CAN-2005-0667 to this issue.
Users of Sylpheed should upgrade to this updated package, which contains a backported patch, and is not vulnerable to this issue.