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.

In imap_scan_tree_recursive in Claws Mail through 3.17.6, a malicious IMAP server can trigger stack consumption because of unlimited recursion into subdirectories during a rebuild of the folder tree.

common/session.c in Claws Mail before 3.17.6 has a protocol violation because suffix data after STARTTLS is mishandled.

Stack-based buffer overflow in the conv_euctojis function in codeconv.c in Claws Mail 3.13.1 allows remote attackers to have unspecified impact via a crafted email, involving Japanese character set conversion. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-8614.

Multiple stack-based buffer overflows in the (1) conv_jistoeuc, (2) conv_euctojis, and (3) conv_sjistoeuc functions in codeconv.c in Claws Mail before 3.13.1 allow remote attackers to have unspecified impact via a crafted email, involving Japanese character set conversion.

plugins/rssyl/feed.c in Claws Mail before 3.10.0 disables the CURLOPT_SSL_VERIFYHOST check for CN or SAN host name fields, which makes it easier for remote attackers to spoof servers and conduct man-in-the-middle (MITM) attacks.

The strchr function in procmime.c in Claws Mail (aka claws-mail) 3.8.1 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) via a crafted email.

sylprint.pl in claws mail tools (claws-mail-tools) allows local users to overwrite arbitrary files via a symlink attack on the sylprint.[USER].[PID] temporary file.