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Active Directory - Tricks

Kerberos Clock Synchronization

In Kerberos, time is used to ensure that tickets are valid. To achieve this, the clocks of all Kerberos clients and servers in a realm must be synchronized to within a certain tolerance. The default clock skew tolerance in Kerberos is 5 minutes, which means that the difference in time between the clocks of any two Kerberos entities should be no more than 5 minutes.

  • Detect clock skew automatically with nmap 
    $ nmap -sV -sC 10.10.10.10
clock-skew: mean: -1998d09h03m04s, deviation: 4h00m00s, median: -1998d11h03m05s
  • Compute yourself the difference between the clocks 
    nmap -sT 10.10.10.10 -p445 --script smb2-time -vv
  • Fix #1: Modify your clock 
    sudo date -s "14 APR 2015 18:25:16" # Linux
net time /domain /set # Windows
  • Fix #2: Fake your clock 
    faketime -f '+8h' date

References