* Linux Mint 4.15 Kernel and NTLMv2 account lockout with empty string password.
@ 2020-03-20 10:19 Stefan Metzmacher
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From: Stefan Metzmacher @ 2020-03-20 10:19 UTC (permalink / raw)
To: linux-cifs; +Cc: Samba Technical
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I recently noticed the following problem with a 4.15 Kernel
on Linux Mint:
/etc/fstab has something like this:
> //172.31.9.132/share1 /media/cifs/share1 cifs vers=1.0,credentials=/media/cifs/cifsmount.creds.txt 0 1
> //172.31.9.132/share2 /media/cifs/share2 cifs vers=1.0,credentials=/media/cifs/cifsmount.creds.txt 0 1
> //172.31.9.132/share3 /media/cifs/share3 cifs vers=1.0,credentials=/media/cifs/cifsmount.creds.txt 0 1
> //172.31.9.132/share4 /media/cifs/share4 cifs vers=1.0,credentials=/media/cifs/cifsmount.creds.txt 0 1
172.31.9.132 is a Windows Server in a Domain with Samba AD-DCs.
The initial mounting works fine, but after some time Samba
logs WRONG_PASSWORD and finally ACCOUNT_LOCKED_OUT.
From various clients this happens about once per hour!
In order to debug this I extended wireshark.
wireshark was already able to decrypt NTLMSSP encryption
when an NTLMSSP password and/or a keytab is provided.
I extended that in order add some useful expert info
that shows which NTHASH was used for a given authentication.
That is also available with an Schannel encrypted Netr_LogonSamLogon*
call. This landed in wiresharks master branch a few days ago.
The customers capture didn't show that information,
which meant that the client used a wrong password
when it got LOGON_FAILURE from the Windows fileserver
(because that got WRONG_PASSWORD or ACCOUNT_LOCKED_OUT
from the AD-DC).
I cross checked that with smbclient and there wireshark
showed the correct password was used.
This is very strange and I had the idea to just check
if maybe an empty string password was used by the client.
So I created a keytab with the NTHASH of an empty string.
And wireshark showed that this NTHASH was actually used...
Has anybody seen this before? We'll retry this with a newer
kernel next week...
Otherwise any idea how to debug that?
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2020-03-20 10:19 Linux Mint 4.15 Kernel and NTLMv2 account lockout with empty string password Stefan Metzmacher
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