With the Red Hat Enterprise Linux 7.4 release of the openssh package, the default value of the GSSAPIStrictAcceptorCheck configuration option in the OpenSSH server was changed to "No". Consequently, unexpected failure states occured in incomplete Kerberos-configured environments. With this update, the GSSAPIStrictAcceptorCheck default value has been changed back to "Yes", and the failures no longer occur in the described scenario.
Description of problem:
With the 7.4 release of openssh, the "GSSAPIStrictAcceptorCheck" configuration option default state changed.
# rpm -q openssh && sshd -T | grep -i GSSAPIStrictAcceptorCheck
openssh-6.6.1p1-35.el7_3.x86_64
gssapistrictacceptorcheck yes
Versus:
# rpm -q openssh && sshd -T | grep -i GSSAPIStrictAcceptorCheck
openssh-7.4p1-12.el7_4.x86_64
gssapistrictacceptorcheck no
This causes incomplete Kerberos configured environments to exhibit unexpected failure states. Such as the following where the server side is not properly configured for the Kerberos domain:
# ssh -v host.example.com
<snip>
debug1: Enabling compatibility mode for protocol 2.0^M
debug1: Local version string SSH-2.0-OpenSSH_7.4^M
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4^M
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000^M
debug1: Authenticating to host.example.com:22 as 'root'^M
debug1: Offering GSSAPI proposal: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-gex-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group1-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group14-sha1-eipGX3TCiQSrx573bT1o1Q==^M
debug1: SSH2_MSG_KEXINIT sent^M
debug1: SSH2_MSG_KEXINIT received^M
debug1: kex: algorithm: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==^M
debug1: kex: host key algorithm: ecdsa-sha2-nistp256^M
debug1: kex: server->client cipher: chacha20-poly1305 MAC: <implicit> compression: none^M
debug1: kex: client->server cipher: chacha20-poly1305 MAC: <implicit> compression: none^M
debug1: kex: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g== need=64 dh_need=64^M
debug1: kex: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g== need=64 dh_need=64^M
debug1: Doing group exchange
^M
debug1: Calling gss_init_sec_context^M
debug1: Delegating credentials^M
ssh_packet_read: Connection closed^M
Version-Release number of selected component (if applicable):
openssh-7.4p1-11.el7 and above
How reproducible:
Simple
Steps to Reproduce:
1. Deploy openssh-server from 7.3 such as openssh-6.6.1p1-35.el7_3.x86_64
2. sshd -T | grep gssapistrictacceptorcheck
3. Update to openssh-server from 7.4 such as openssh-7.4p1-11.el7 or above
Actual results:
gssapistrictacceptorcheck no
Expected results:
gssapistrictacceptorcheck yes
Additional info:
sigh ... there was a bug in upstream that the documentation was saying default is "yes", though it was not in the code. It is fixed in master and even in openssh-7.5, but not in 7.4, which we picked up (and missed).
https://github.com/openssh/openssh-portable/commit/13bd2e2
So your patch is something that will actually appear in 7.5 for sure and in Z-stream if we will get it approved. Thanks for the investigation, ideas and testing.
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-2018:0980
Description of problem: With the 7.4 release of openssh, the "GSSAPIStrictAcceptorCheck" configuration option default state changed. # rpm -q openssh && sshd -T | grep -i GSSAPIStrictAcceptorCheck openssh-6.6.1p1-35.el7_3.x86_64 gssapistrictacceptorcheck yes Versus: # rpm -q openssh && sshd -T | grep -i GSSAPIStrictAcceptorCheck openssh-7.4p1-12.el7_4.x86_64 gssapistrictacceptorcheck no This causes incomplete Kerberos configured environments to exhibit unexpected failure states. Such as the following where the server side is not properly configured for the Kerberos domain: # ssh -v host.example.com <snip> debug1: Enabling compatibility mode for protocol 2.0^M debug1: Local version string SSH-2.0-OpenSSH_7.4^M debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4^M debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000^M debug1: Authenticating to host.example.com:22 as 'root'^M debug1: Offering GSSAPI proposal: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-gex-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group1-sha1-eipGX3TCiQSrx573bT1o1Q==,gss-group14-sha1-eipGX3TCiQSrx573bT1o1Q==^M debug1: SSH2_MSG_KEXINIT sent^M debug1: SSH2_MSG_KEXINIT received^M debug1: kex: algorithm: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==^M debug1: kex: host key algorithm: ecdsa-sha2-nistp256^M debug1: kex: server->client cipher: chacha20-poly1305 MAC: <implicit> compression: none^M debug1: kex: client->server cipher: chacha20-poly1305 MAC: <implicit> compression: none^M debug1: kex: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g== need=64 dh_need=64^M debug1: kex: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g== need=64 dh_need=64^M debug1: Doing group exchange ^M debug1: Calling gss_init_sec_context^M debug1: Delegating credentials^M ssh_packet_read: Connection closed^M Version-Release number of selected component (if applicable): openssh-7.4p1-11.el7 and above How reproducible: Simple Steps to Reproduce: 1. Deploy openssh-server from 7.3 such as openssh-6.6.1p1-35.el7_3.x86_64 2. sshd -T | grep gssapistrictacceptorcheck 3. Update to openssh-server from 7.4 such as openssh-7.4p1-11.el7 or above Actual results: gssapistrictacceptorcheck no Expected results: gssapistrictacceptorcheck yes Additional info: