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DescriptionLeonard 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.
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 ***