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Re: SSH LocalForward
From: sevo () inm de (Sevo Stille)
Date: Sun, 3 Aug 1997 01:03:25 +0200


Von: Kristof Van Damme <aeneas () sesuadra org>
...
I bumped into a weird 'feature' of ssh 1.2.20. When I run:
...
the port must be available). When I connect to it I get a normal
redirection to remotehost:80 over the secure channel. This means however
that a non-root user is able to open privileged ports on the localhost and
redirect them. Is this normal? I checked it on Linux and Solaris.

From a quick glance across the source, ssh rejects attempts to forward privileged
ports for non-root users while parsing the command line arguments - the config file
is read further down in the code, without performing a similar test. The immediate
fix is chmod -s (which will get rid of potential similar holes in ssh as well...) - the
more reasonable method is to move the check into add_local_forward():

 --- readconf.c  Sun Aug  3 00:55:40 1997
+++ readconf.c.orig     Sun Aug  3 00:57:21 1997
@@ -204,11 +204,6 @@
   Forward *fwd;
   if (options->num_local_forwards >= SSH_MAX_FORWARDS_PER_DIRECTION)
     fatal("Too many local forwards (max %d).", SSH_MAX_FORWARDS_PER_DIRECTION);
-  if (port < 1024 && original_real_uid != UID_ROOT)
-  {
-     fatal("Privileged ports can only be forwarded by root.\n");
-     exit(1);
-  }
   fwd = &options->local_forwards[options->num_local_forwards++];
   fwd->port = port;
   fwd->host = xstrdup(host);



Sevo



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