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Bug 1373835

Summary: Ciphers and MACs enabled by default differ from upstream OpenSSH 6.7 with security implications.
Product: Red Hat Enterprise Linux 7 Reporter: Jakub Svoboda <jsvoboda>
Component: opensshAssignee: Jakub Jelen <jjelen>
Status: CLOSED ERRATA QA Contact: Alicja Kario <hkario>
Severity: unspecified Docs Contact: Mirek Jahoda <mjahoda>
Priority: unspecified    
Version: 7.2CC: ahecox, ajb, freshman, leonard-rh-bugzilla, mgrepl, nmavrogi, phil, szidek, toracat, vdanen
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: openssh-7.4p1-1.el7 Doc Type: Deprecated Functionality
Doc Text:
OpenSSH upstream removes several ciphers with questionable security from the release. This update is trying to follow this trend while leaving most of the backward compatibility. Since last update we removed from Server&Client proposal: * Hostkey algorithms: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com (deprecated) * Ciphers: arcfour256,arcfour128,arcfour,rijndael-cbc@lysator.liu.se (RC4 is broken, rijndael-cbc quite much unused alias for AES) * MACs: hmac-md5,hmac-md5-96,hmac-md5-96-etm@openssh.com,hmac-md5-etm@openssh.com,hmac-ripemd160,hmac-ripemd160-etm@openssh.com,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-sha1-96-etm@openssh.com (MD5, truncated SHA-1, RIPEMD160) Since last update we removed from client proposal: * Ciphers: blowfish-cbc,cast128-cbc,3des-cbc (in addition to the above) - non-essential and possibly broken.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2017-08-01 18:42:47 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: 1335929, 1377248, 1417264    

Description Jakub Svoboda 2016-09-07 08:54:18 UTC 
Description of problem:
The default configuration of openssh-server 6.7 disables some of the supported Ciphers and MACs. "In particular, CBC ciphers and arcfour* are disabled by default." [1]. MACs that are disabled by default are *md5*, *ripemd160*, *sha1*96*.

Version-Release number of selected component (if applicable):
openssh-6.6.1p1-25.el7_2

How reproducible:
always

Steps to Reproduce:

1. yum distribution-synchronization  # just to ensure the latest RHEL is installed

2. rm /etc/ssh/sshd_config

3. yum reinstall openssh-server      # recreates default /etc/ssh/sshd_config

4. sshd -T | grep -i "Ciphers\|MACs" # lists currently enabled Ciphers and MACs


Actual results:
The default enabled Ciphers include *cbc*, *arcfour*.
The default enabled MACs include *md5*, *ripemd160*, *sha1*96*.

Actual results of the command sshd -T | grep -i "Ciphers\|MACs"
ciphers 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,arcfour128,arcfour256,aes128-cbc,aes192-cbc,aes256-cbc,rijndael-cbc.se,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm,aes256-gcm,chacha20-poly1305
macs hmac-sha1,hmac-sha1-96,hmac-sha2-256,hmac-sha2-512,hmac-md5,hmac-md5-96,hmac-ripemd160,hmac-ripemd160,umac-64,umac-128,hmac-sha1-etm,hmac-sha1-96-etm,hmac-sha2-256-etm,hmac-sha2-512-etm,hmac-md5-etm,hmac-md5-96-etm,hmac-ripemd160-etm,umac-64-etm,umac-128-etm


Expected results:
Defaults follow recent OpenSSH upstream versions.
These Ciphers are disabled by default: *cbc*, *arcfour*.
These MACs are disabled by default: *md5*, *ripemd160*, *sha1*96*.

Expected results of the command sshd -T | grep -i "Ciphers\|MACs"
ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm,aes256-gcm,chacha20-poly1305
macs hmac-sha1,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160,umac-64,umac-128,hmac-sha1-etm,hmac-sha2-256-etm,hmac-sha2-512-etm,hmac-ripemd160-etm,umac-64-etm,umac-128-etm


Additional info:
* Red Hat's KB article about insecure Ciphers and MACs recommends non-default values [3]
* The latest RH-shipped version is 6.6.1p1 / 5.3p1; however it would be good to follow current security recommendations regarding the defaults.
* We have a Red Hat Insights rule for OpenSSH hardening that would get activated once the defaults in the openssh-server package are fixed. Red Hat Insights is a service to notify enrolled customers about problems on their systems. It is best when customers are not alerted about RHEL-default values.
* OpenSSH 6.7 through 7.1 disables hmac-sha1-etm and hmac-sha1 but OpenSSH 7.2 reenables it.
References:
[1] http://www.openssh.com/txt/release-6.7
[2] http://www.openssh.com/txt/release-7.2
[3] https://access.redhat.com/solutions/420283
Comment 5 Jakub Jelen 2017-01-30 07:50:42 UTC 
*** Bug 1417263 has been marked as a duplicate of this bug. ***
Comment 12 errata-xmlrpc 2017-08-01 18:42:47 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, 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/RHSA-2017:2029