textview_uri_security_check in textview.c in Claws Mail before 3.18.0, and Sylpheed through 3.7.0, does not have sufficient link checks before accepting a click.

Format string vulnerability in the inc_put_error function in src/inc.c in Sylpheed 2.4.4, and Sylpheed-Claws (Claws Mail) 1.9.100 and 2.10.0, allows remote POP3 servers to execute arbitrary code via format string specifiers in crafted replies.

Sylpheed-Claws before 2.2.2 and Sylpheed before 2.2.6 allow remote attackers to bypass the URI check functionality and makes it easier to conduct phishing attacks via a URI that begins with a space character.

Buffer overflow in Sylpheed before 1.0.3 and other versions before 1.9.5 allows remote attackers to execute arbitrary code via an e-mail message with certain headers containing non-ASCII characters that are not properly handled when the user replies to the message.

Format string vulnerability in send_message.c for Sylpheed-claws 0.9.4 through 0.9.6 allows remote SMTP servers to cause a denial of service (crash) in sylpheed via format strings in an error message.