RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
Bug 1417264 - OpenSSH will negotiate MD5 HMAC in default configuration [RFE] provide safe default
Summary: OpenSSH will negotiate MD5 HMAC in default configuration [RFE] provide safe d...
Keywords:
Status: CLOSED DUPLICATE of bug 1373836
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: openssh
Version: 6.8
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Jakub Jelen
QA Contact: BaseOS QE Security Team
URL:
Whiteboard:
Depends On: 1373835 1417263
Blocks:
TreeView+ depends on / blocked
 
Reported: 2017-01-27 17:47 UTC by Leonard den Ottolander
Modified: 2017-02-01 15:09 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of: 1417263
Environment:
Last Closed: 2017-02-01 15:09:21 UTC
Target Upstream Version:
Embargoed:


Attachments (Terms of Use)

Description Leonard den Ottolander 2017-01-27 17:47:00 UTC
+++ This bug was initially created as a clone of Bug #1417263 +++

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 07:42:23 UTC
> MD5 has been considered insecure for quite some time now.

That is true for cryptographic signature usage, but not for HMACs (integrity checks usage).

Thank you for your input, but this is already handled in the bug #1373836, which will be out soon. Let me know if there is something more you would like to achieve or I can close the bug as a duplicate.

Comment 3 Leonard den Ottolander 2017-02-01 15:02:50 UTC
Even if HMACs are not quite as susceptible it's just plain stupid to keep known broken primitives around as defaults.

As you are well aware attacks in crypto only ever get better, so over time things that were barely acceptable might very well become totally unsafe.

NIST never even standardized MD5 as a HMAC for use in TLS, supposedly because of it utter brokenness.

10 years have gone by, and is quite possible that attacks that seemed infeasible 10 years ago are now quite possible seeing that state financed adversaries have budgets of billions of dollars per year.

But I agree this is a dup of #1373836 so I'll hook on to that report.

Comment 4 Jakub Jelen 2017-02-01 15:09:21 UTC

*** This bug has been marked as a duplicate of bug 1373836 ***


Note You need to log in before you can comment on or make changes to this bug.