To use CVS over SSH one must generally set environment variable CVS_RSH like

SET CVS_RSH=ssh

  This is good for unices, but no good in OS/2 where CVS is patched to add a
/b switch to rsh command line to put it to binary mode. This switch is required
for OS/2 rsh, but it wont work for ssh. Here is an elegant workaround for this
problem proposed by Clemens Lanthaler:

SET CVS_RSH=D:\TOOLS\openssh\cvs-ssh.cmd

cvs-ssh.cmd:
ssh %1 %3 %4 %5 %6

  As you see, the cvs-ssh.cmd just drops a /b switch which comes second from 
cvs.exe.