OK, this will not work for Net::SSH::Perl -- I don't have that module installed, and I hear it is nontrivial on a Solaris platform. Besides, at some point I need to go home. But your problem intrigued me because I currently had no way to handle problems with my existing Net::SSH use. I played for quite a while with IO::Capture before I realized that the output from the Net::SSH->ssh() method was neither STDERR nor STDOUT for my script.

So I wrote a little program using Net::SSH->sshopen3() which seems to work pretty well in both the happy and unhappy cases:

#!/usr/local/bin/perl -w

use Net::SSH qw(sshopen3);
use strict;

Main: {
  my $host = 'nobody@nowhere.com';
  my @command = ('ls -al;', 'echo Howdy!');

  my $reader = IO::File->new();
  my $writer = IO::File->new();
  my $error  = IO::File->new();

  sshopen3( $host, $writer, $reader, $error, @command ) or die $!;

  local $/ = undef;
  my $output_stream = <$reader>;
  my $error_stream = <$error>;

  if ( length $error_stream ) {
    print "SSH error: $error_stream";
  }
  if ( length $output_stream ) {
    print "SSH output: $output_stream";
    }
  
}
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If you use the $host string I have provided, you should see a message to that effect in $error_stream, which you could capture and reformat for display in your CGI script. I hope that helps you at least a little.