Mailing List Archive

[Bug 3313] CVE-2020-14145 - will it get fixed?
https://bugzilla.mindrot.org/show_bug.cgi?id=3313

m.kaiser@bmlv.gv.at changed:

What |Removed |Added
----------------------------------------------------------------------------
URL| |https://docs.ssh-mitm.at/CV
| |E-2020-14145.html

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[Bug 3313] CVE-2020-14145 - will it get fixed? [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3313

Damien Miller <djm@mindrot.org> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |djm@mindrot.org
Resolution|--- |WONTFIX

--- Comment #1 from Damien Miller <djm@mindrot.org> ---
First, we consider the automatic ordering of host key algorithms an
important feature for security. It provides continuity of trust by
clients across changes in default algorithm preference in ssh and
servers offering hostkeys of different types.

Disabling this feature wholesale would IMO result in a net *loss* of
security as it would force more connections that already have learned a
hostkey to accept a new one of a different algorithm, thereby
needlessly exposing them to MITM risk.

That being said, commit b3855ff (shipped in openssh-8.4) adjusted the
ordering to always use the default if the client has learned a hostkey
matching the best-preference algorithm. openssh-8.5 enabled
UpdateHostkeys by default (with some restrictions) so most users will
automatically learn a best-preference hostkey if one is available at
the server. Between these, most users should end up using the default
algorithm list.

Speaking for myself - I plan to relax the restrictions around
UpdateHostkeys' activation, but do not plan to take other action around
this "vulnerability". In particular, I do not intend to offer an option
to force the use of the default cipher list. IMO too many users would
flip it thinking it solved a security problem when the situation is
actually far more subtle and the reverse is likely the case.

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[Bug 3313] CVE-2020-14145 - will it get fixed? [ In reply to ]
https://bugzilla.mindrot.org/show_bug.cgi?id=3313

--- Comment #2 from m.kaiser@bmlv.gv.at ---
Thanks for the answer. Now I understand the problem better.

Mitigation might be possible, but with the risk of a changing
fingerprint due to different preferred algorithms. For most users, this
might be more error prone and it's more likely that the users accepts a
wrong fingerprint.

So the only real mitigation is setting up a CA and using certificates,
or is this a wrong assumption?

The documentation is updated with your answer and the recommendation
how to mitigate this vulnerability was changed.

Sorry, that I have escalated this vulnerability.

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