Re: openssh 4.2p1 zlib compression broken for old clients

On Wed Oct 26 10:06:55 2005, Harald Koenig wrote:
>
> Hello OpenSSH developers,
>
> openssh 4.2p1 breaks old openssh clients up to 3.4p1 when they try to use compression:
>

This is spelt out pretty clearly in the ChangeLog for 4.2p1 and (if I recall
correctly) in the release announcement on this list. Admittedly, the
sshd_config(5) man page does not appear to call out this issue.

Set Compression=yes in your sshd_config and the old clients should behave.

> # ssh-3.4p1 -C remote-host-with-4.2p1 pwd
> no matching comp found: client zlib server none,zlib@openssh.com
>
> option "-vv" shows
>
> ...
> debug2: kex_parse_kexinit: zlib
> ...
> debug2: kex_parse_kexinit: none,zlib@openssh.com
> ...
> debug2: mac_init: found hmac-md5
> no matching comp found: client zlib server none,zlib@openssh.com
>
> using the small patch below makes the old ssh clients happy again with option "-C"
>
>
> -------------------------------------------------------------------------------
> --- openssh-4.2p1/sshd.c~ 2005-10-05 17:58:21.000000000 +0200
> +++ openssh-4.2p1/sshd.c 2005-10-26 18:17:44.000000000 +0200
> @@ -2014,7 +2014,7 @@
> myproposal[PROPOSAL_COMP_ALGS_STOC] = "none";
> } else if (options.compression == COMP_DELAYED) {
> myproposal[PROPOSAL_COMP_ALGS_CTOS] =
> - myproposal[PROPOSAL_COMP_ALGS_STOC] = "none,zlib@openssh.com";
> + myproposal[PROPOSAL_COMP_ALGS_STOC] = "none,zlib@openssh.com,zlib";
> }
>
> myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = list_hostkey_types();
> -------------------------------------------------------------------------------
>
>
> Harald Koenig
>
> PS: yes I know about the security issues using such old ssh clients, but it's
> only used in fairly protected small internal customer networks, and the customer
> insists not to change anything in those environments running the old ssh clients...
> (the surrounding environment is pretty well maintained which is the reason for
> the 4.2p1 sshd;-)
> --
> "I hope to die ___ _____
> before I *have* to use Microsoft Word.", 0--,| /OOOOOOO\
> Donald E. Knuth, 02-Oct-2001 in Tuebingen. <_/ / /OOOOOOOOOOO\
> \ \/OOOOOOOOOOOOOOO\
> \ OOOOOOOOOOOOOOOOO|//
> Harald Koenig \/\/\/\/\/\/\/\/\/
> science+computing ag // / \\ \
> koenig@science-computing.de ^^^^^ ^^^^^
>
> _______________________________________________
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> openssh-unix-dev@mindrot.org
> http://www.mindrot.org/mailman/listi...enssh-unix-dev
>


--
Iain Morgan

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