Bug 1816226

Summary:	Weak GSSAPI key exchange methods enabled by default [openssh]
Product:	Red Hat Enterprise Linux 8	Reporter:	Jakub Jelen <jjelen>
Component:	openssh	Assignee:	Jakub Jelen <jjelen>
Status:	CLOSED ERRATA	QA Contact:	Ondrej Moriš <omoris>
Severity:	unspecified	Docs Contact:
Priority:	medium
Version:	8.4	CC:	cwarfiel, dwalsh, jjelen, omoris, plautrba, tmraz
Target Milestone:	rc	Keywords:	Triaged
Target Release:	8.0
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	openssh-8.0p1-5.el8	Doc Type:	Enhancement
Doc Text:	Feature: New GSSAPI key exchange methods using SHA2 from RFC 8732 are enabled by default. Reason: RHEL 8 contains implementation of the new GSSAPI key exchange methods since 8.0, but only the SHA1 were enabled by default because the specification was not finalized. Now, the specification is published so the new methods are enabled by default (which also depends on a change in crypto policies). Result: The new SHA2-based GSSAPI key exchange methods are available and usable by default.	Story Points:	---
Clone Of:	1666781
Clones:	1816253 (view as bug list)		Environment:
Last Closed:	2020-11-04 01:32:00 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1666781
Bug Blocks:	1816253

Description Jakub Jelen 2020-03-23 15:29:52 UTC

+++ This bug was initially created as a clone of Bug #1666781 +++

The build of OpenSSH in Fedora carries patches to enable GSSAPI key exchange.  Hurrah, when this is used, the need to manually verify host keys is removed.

The manual says that the default value for setting GSSAPIKexAlgorithms is “gss-gex-sha1-,gss-group14-sha1-”.  However, https://datatracker.ietf.org/doc/draft-ietf-curdle-ssh-kex-sha2/ says that gss-gex-sha1- is weak and "SHOULD NOT be used".  I suggest that it be disabled by default, and that some of the newer methods such as gss-curve25519-sha256-, gss-nistp256-sha256-, gss-group14-sha256-
be enabled by default instead.

--- Additional comment from Jakub Jelen on 2019-01-16 16:28:20 CET ---

Hello and thank you for your interest. This is indeed planned, but we are waiting for finalizing and approving the draft defining the new gssapi key exchange methods before enabling them to the world:

https://tools.ietf.org/html/draft-ietf-curdle-gss-keyex-sha2-08

Generally, the GEX methods are not advised these days and once we will have something better, we will certainly try to disable them.

Actually I am not quite sure if I saw your referenced draft before, but it looks like it is stalled, the current version expired and it does not look like moving forward to be accepted as a RDC any time soon. Actually it does not say anything new to me.

I will leave this bug open to keep track of things and make sure I will update the list when the drafts will get approved.

--- Additional comment from Jakub Jelen on 2020-03-23 15:27:14 CET ---

FYI, the RFC 8732 was published so I would like to enable these soon in Fedora.

[1] https://tools.ietf.org/html/rfc8732

--- Additional comment from Jakub Jelen on 2020-03-23 16:24:34 CET ---

First step is enabling them in Crypto policy. The issue was filled here as it does not look like completely straight-forward:

https://gitlab.com/redhat-crypto/fedora-crypto-policies/-/issues/19

Comment 8 errata-xmlrpc 2020-11-04 01:32:00 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (openssh bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:4439