Bug 1417263

Summary:	OpenSSH will negotiate MD5 HMAC in default configuration [RFE] provide safe default
Product:	Red Hat Enterprise Linux 7	Reporter:	Leonard den Ottolander <leonard-rh-bugzilla>
Component:	openssh	Assignee:	Jakub Jelen <jjelen>
Status:	CLOSED DUPLICATE	QA Contact:	BaseOS QE Security Team <qe-baseos-security>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	7.3	CC:	phil
Target Milestone:	rc	Keywords:	FutureFeature
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:
Clones:	1417264 (view as bug list)		Environment:
Last Closed:	2017-01-30 07:50:42 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:
Bug Blocks:	1417264

Description Leonard den Ottolander 2017-01-27 17:45:55 UTC

OpenSSH on both RHEL 7 (openssh-6.6.1p1-31.el7) and RHEL 6 (openssh-5.3p1-118.1.el6_8) will by default negotiate an MD5 HMAC. MD5 has been considered insecure for quite some time now.

C6 client, C7 server: (C in CentOS)

debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-ctr hmac-md5 none
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-ctr hmac-md5 none

C7 client & server:

debug2: mac_setup: setup hmac-md5-etm
debug1: kex: server->client aes128-ctr hmac-md5-etm none
debug2: mac_setup: setup hmac-md5-etm
debug1: kex: client->server aes128-ctr hmac-md5-etm none

Default order on C7:

debug2: kex_parse_kexinit: hmac-md5-etm,hmac-sha1-etm,umac-64-etm,umac-128-etm,hmac-sha2-256-etm,hmac-sha2-512-etm,hmac-ripemd160-etm,hmac-sha1-96-etm,hmac-md5-96-etm,hmac-md5,hmac-sha1,umac-64,umac-128,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160,hmac-sha1-96,hmac-md5-96

Default order on C6:

debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,umac-64,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160,hmac-sha1-96,hmac-md5-96

I would like to suggest to add the following line to both ssh_config and sshd_config:

RHEL 7:

MACs hmac-sha2-512-etm,hmac-sha2-512,hmac-sha2-256-etm,hmac-sha2-256,hmac-sha1-etm,hmac-sha1,hmac-ripemd160-etm,hmac-ripemd160,hmac-ripemd160,umac-128,umac-128-etm,hmac-sha1-96-etm,hmac-sha1-96,umac-64-etm,umac-64

RHEL 6:

MACS hmac-sha2-512,hmac-sha2-256,hmac-sha1,hmac-ripemd160,hmac-ripemd160,hmac-sha1-96,umac-64

Even if this is not the desired order - note that the default order appears to be quite random itself - the fact that this option is available in the configuration files should give the administrator enough of a clue.

Comment 2 Jakub Jelen 2017-01-30 07:50:42 UTC

This is already discussed in the bug #1373835 (see my comment in the cloned bug #1417264). Lets continue discussion there.

*** This bug has been marked as a duplicate of bug 1373835 ***