Simon G. Tatham reports:
Many versions of PSCP 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.[...] you can work around it in a vulnerable PSCP by using the -sftp option to force the use of the newer SFTP protocol, provided your server supports that protocol.