Security Focus: Find User Accounts Configured for DES Encryption


Once more, with feeling: extended support for Windows Server 2003 ends on July 14, 2015…

Hopefully, you’ve already upgraded your domain controllers to at least Windows Server 2008 R2. If you haven’t, there are security enhancements to be aware of. Here’s more information:

W2K3 to W2K8 and W2K8R2 Active Directory Upgrade Considerations

 

One of those enhancements is the disabling of DES encryption for Kerberos authentication. If you have user accounts, most likely service accounts, configured to just use DES there’ll be authentication ‘trouble at mill’!

How do you check for these accounts?

Get-ADUser -Filter {UserAccountControl -band 0x200000}

That was easy!

User Accounts have different options that can be set to control security settings. In Active Directory Users and Computers most of these options can be found in the ‘Account’ tab of the user object dialogue box, under ‘Account options’:

 

  

In the above window, the user is set to use DES encryption. This setting is stored as part of a binary mask in the ‘UserAccountControl’ attribute of the user object. In the binary mask, each positional bit represents a different possible user account option that can be switched on or switched off. Like a light switch – when switched on, the option is active. These settings can be queried using PowerShell’s ‘binary And’ (-band) operator. The hexadecimal setting for DES encryption is 0x200000 and we use -band to check that it is present (switched on) in the binary mask.

 

Here are other values you could check for with the aid of a filter and Get-ADUser:

Property Flag Value in Hexadecimal Value in Decimal
SCRIPT 0x0001 1
ACCOUNTDISABLE 0x0002 2
HOMEDIR_REQUIRED 0x0008 8
LOCKOUT 0x0010 16
PASSWD_NOTREQD 0x0020 32
PASSWD_CANT_CHANGE 0x0040 64
ENCRYPTED_TEXT_PWD_ALLOWED 0x0080 128
TEMP_DUPLICATE_ACCOUNT 0x0100 256
NORMAL_ACCOUNT 0x0200 512
INTERDOMAIN_TRUST_ACCOUNT 0x0800 2048
WORKSTATION_TRUST_ACCOUNT 0x1000 4096
SERVER_TRUST_ACCOUNT 0x2000 8192
DONT_EXPIRE_PASSWORD 0x10000 65536
MNS_LOGON_ACCOUNT 0x20000 131072
SMARTCARD_REQUIRED 0x40000 262144
TRUSTED_FOR_DELEGATION 0x80000 524288
NOT_DELEGATED 0x100000 1048576
USE_DES_KEY_ONLY 0x200000 2097152
DONT_REQ_PREAUTH 0x400000 4194304
PASSWORD_EXPIRED 0x800000 8388608
TRUSTED_TO_AUTH_FOR_DELEGATION 0x1000000 16777216
PARTIAL_SECRETS_ACCOUNT 0x04000000 67108864

 

You’re quite at liberty to combine them. This one tests for users who have the following set: ‘Password never expires’, ‘Store password using reversible encryption’ and ‘Use Kerberos DES encryption types for this account’.

$COMBINED_VALUE = 0x10000 + 0x0080 + 0x200000

Get-ADUser -Filter {UserAccountControl -band $COMBINED_VALUE}

 

One would hope that this query never returns objects!

TTFN!

Comments (2)

  1. Anonymous says:

    thank you

  2. Christian @ C&A says:

    Thanks for this great article