Introduction to Active Directory - https://academy.hackthebox.com/module/74/section/1350

Tags

Top Highlights

• These include LM, NTLM, NTLMv1, and NTLMv2. LM and NTLM here are the hash names, and NTLMv1 and NTLMv2 are authentication protocols that utilize the LM or NT hash.

• If in use, they are stored in the SAM database on a Windows host and the NTDS.DIT database on a Domain Controller. Due to significant security weaknesses in the hashing algorithm used for LM hashes, it has been turned off by default since Windows Vista/Server 2008.

• Passwords using LM are limited to a maximum of 14 characters. Passwords are not case sensitive and are converted to uppercase before generating the hashed value, limiting the keyspace to a total of 69 characters making it relatively easy to crack these hashes using a tool such as Hashcat.

• Two DES keys are created from each chunk. These chunks are then encrypted using the string KGS!@#$%, creating two 8-byte ciphertext values. These two values are then concatenated together, resulting in an LM hash. This hashing algorithm means that an attacker only needs to brute force seven characters twice instead of the entire fourteen characters, making it fast to crack LM hashes on a system with one or more GPUs. If a password is seven characters or less, the second half of the LM hash will always be the same value and could even be determined visually without even needed tools such as Hashcat.

• used on modern Windows systems

• It is a challenge-response authentication protocol and uses three messages to authenticate: a client first sends a NEGOTIATE_MESSAGE to the server, whose response is a CHALLENGE_MESSAGE to verify the client's identity. Lastly, the client responds with an AUTHENTICATE_MESSAGE.

• The protocol has two hashed password values to choose from to perform authentication: the LM hash (as discussed above) and the NT hash, which is the MD4 hash of the little-endian UTF-16 value of the password.

• Even though they are considerably stronger than LM hashes (supporting the entire Unicode character set of 65,536 characters), they can still be brute-forced offline relatively quickly using a tool such as Hashcat.

• Longer NTLM hashes can be more challenging to crack depending on the password chosen, and even long passwords (15+ characters) can be cracked using an offline dictionary attack combined with rules.

• NTLM is also vulnerable to the pass-the-hash attack, which means an attacker can use just the NTLM hash (after obtaining via another successful attack) to authenticate to target systems where the user is a local admin without needing to know the cleartext value of the password.

• The server sends the client an 8-byte random number (challenge), and the client returns a 24-byte response. These hashes can NOT be used for pass-the-hash attacks.

• NTLMv2 sends two responses to the 8-byte challenge received by the server. These responses contain a 16-byte HMAC-MD5 hash of the challenge, a randomly generated challenge from the client, and an HMAC-MD5 hash of the user's credentials. A second response is sent, using a variable-length client challenge including the current time, an 8-byte random value, and the domain name.

• In an AD environment, the authentication methods mentioned in this section and the previous require the host we are trying to access to communicate with the "brains" of the network, the Domain Controller.

• to solve the potential issue of a domain-joined host being unable to communicate with a domain controller (i.e., due to a network outage or other technical issue) and, hence, NTLM/Kerberos authentication not working to access the host in question

• These hashes can be obtained by an attacker or pentester after gaining local admin access to a host and have the following format: $DCC2$10240#bjones#e4e938d12fe5974dc42a90120bd9c90f.