[Bug 1558576] [NEW] OpenSSH Error "Disconnecting: Hash's MIC didn't verify" after upgrading to Ubuntu 16.04

[Brian Knoll]

Public bug reported:

SSH was working fine for years, until I upgraded to Ubuntu 16.04.  When
I upgraded to Ubuntu 16.04, the openssh-server stopped accepting
connections from Ubuntu 14.04 LTS clients, with the following error:

----
Disconnecting: Hash's MIC didn't verify
----

The error above shows up on the client side.  In the server logs, I see
the following:

----
Mar 17 10:01:49 falcon polkitd(authority=local): Unregistered Authentication Agent for unix-process:125110:294284 (system bus name :1.133, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)
Mar 17 10:02:06 falcon sshd[125126]: error: Received disconnect from MY.IP.ADDRESS.HERE port PORTNUMBER:2: Hash's MIC didn't verify [preauth]
Mar 17 10:02:06 falcon sshd[125126]: Disconnected from MY.IP.ADDRESS.HERE port PORTNUMBER [preauth]
----

I am using GSSAPI Key Exchange, and GSSAPI authentication.  So I am not
using public keys or passwords or anything like that; everything is
entirely Kerberos 5.  The problem, also, is only one-way.  In other
words, if I upgrade the server to Ubuntu 16.04, it stops accepting
connections from 14.04 clients, but if I go the other direction and
upgrade the client to Ubuntu 16.04, then it can still authenticate
successfully to an Ubuntu 14.04 machine.

I am more than happy to help debug this, so please let me know what you
suggest and I'll do whatever I can to help.

Thanks,
Brian

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: openssh-server 1:7.2p2-1
ProcVersionSignature: Ubuntu 4.4.0-13.29-generic 4.4.5
Uname: Linux 4.4.0-13-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
Date: Thu Mar 17 10:02:45 2016
InstallationDate: Installed on 2015-05-04 (317 days ago)
InstallationMedia: Ubuntu-Server 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: openssh
UpgradeStatus: Upgraded to xenial on 2016-03-16 (0 days ago)

** Affects: openssh (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug xenial

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https://bugs.launchpad.net/bugs/1558576

Title:
  OpenSSH Error "Disconnecting: Hash's MIC didn't verify" after
  upgrading to Ubuntu 16.04

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