Many versions of PSCP in PuTTY prior to 0.67 have a stack corruption vulnerability in their treatment of the 'sink' direction (i.e. downloading from server to client) of the old-style SCP protocol. In order for this vulnerability to be exploited, the user must connect to a malicious server and attempt to download any file (CVE-2016-2563).
FileZilla was vulnerable to this issue as it bundles a copy of PuTTY. The filezilla package has been updated to version 3.16.1, which fixes this issue and has many other fixes and enhancements.