[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Sat, 30 Mar 2024 15:01:31 -0700
From: Andres Freund <andres@...razel.de>
To: oss-security@...ts.openwall.com
Subject: Re: Re: backdoor in upstream xz/liblzma leading to
ssh server compromise
Hi,
On 2024-03-30 22:46:17 +0100, Axel Beckert wrote:
> On Sat, Mar 30, 2024 at 12:48:50PM -0700, Andres Freund wrote:
> > FWIW, RSA_public_decrypt is reachable, regardless of server configuration,
> > when using certificate based authentication.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Wait, do you really mean SSH keys verified by certificates issued by a
> (usually internal, SSH-specific) certificate authority (CA) for a key?
>
> See e.g.
> https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Certificate-based_Authentication
> what certificate-based authentication in SSH actually means.
>
> From my experience certificate-based SSH authentication (i.e. those
> algorithms with *-cert-* in their names) is rather rare, while simple
> public key authentication (where you just put your according pubkey
> into .ssh/authorized_keys) is very common.
>
> Can you clarify if you really meant that solely certificate based
> authentication (with certificates issued by a CA) triggers that code
> path or if you actually meant all sorts of public key based
> authentication in general?
I meant CA based auth - but note that, from what I can tell, you don't need to
have it set up on the server side or anything. You might not even be able to
disable it. If the client sends a signed key, the signature is loaded and
verified before approved algorithms are checked.
This seems suboptimal regardless of the backdoor issue, so I opened an
enhancement request for openssh: https://bugzilla.mindrot.org/show_bug.cgi?id=3675
I might be misreading the code around some of the details, but I did
experimentally verify that an rsa signature is verified without CA auth being
configured.
Greetings,
Andres Freund
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
