After successfully forcing a victim to authenticate with LM or NTLM to an attacker's server, the attacker can try to recover credentials by capturing and cracking the hash (LM or NTLM hash, a.k.a. response) sent by the victim.


NTLM capture can be combined with any forced authentication attack. Testers should dissociate the name poisoning features that Responder and Inveigh offer from their capturing features. Those tools can be combined with others offering different "authentication forcing" attacks (like IPv6 + name poisoning, MS-RPRN abuse and so on).

Responder (Python) and Inveigh (Powershell) are great tools able to do name poisoning for forced authentication attacks, but also able to capture responses (LM or NTLM hashes) by starting servers waiting for incoming authentications. Once those listening servers are up and ready, the tester can initiate the forced authentication attack.

In order to help the later cracking process, testers need to set the NTLM challenge sent to victims to 1122334455667788.

For Inveigh, it can be defined with a command-line argument. For Responder, testers need to edit the configuration file.

sed -i 's/ Random/ 1122334455667788/g' /PATH/TO/Responder/Responder.conf

From UNIX-like systems, Responder (Python) can be used to start servers listening for NTLM authentications over many protocols (SMB, HTTP, LDAP, FTP, POP3, IMAP, SMTP, ...). Depending on the authenticating principal's configuration, the NTLM authentication can sometimes be downgraded with --lm and --disable-ess in order to obtain NTLMv1 responses.

responder --interface "eth0" --analyze
responder -I "eth0" -A

# with downgrading
responder --interface "eth0" --analyze --lm --disable-ess

Testers should try to force a LM hashing downgrade with Responder. LM and NTLMv1 responses (a.k.a. LM/NTLMv1 hashes) from Responder can easily be cracked with The ntlmv1-multi tool (Python) can be used to convert captured responses to crackable formats by hashcat, and so on.

ntlmv1-multi --ntlmv1 SV01$::BREAKING.BAD:AD1235DEAC142CD5FC2D123ADCF51A111ADF45C2345ADCF5:AD1235DEAC142CD5FC2D123ADCF51A111ADF45C2345ADCF5:1122334455667788

Machine account NT hashes can be used with the Silver Ticket or S4U2self abuse techniques to gain admin access to it.

There are cases where a downgrade attempt will fail and the capture authentication will not be shown. Testers should always try to capture authentication with and without downgrading.

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