📖 What is SMB Relay Attack?
An SMB Relay Attack involves intercepting an SMB authentication request and forwarding it to another server on the network to gain unauthorized access. This attack leverages the lack of SMB signing to impersonate a user without needing to crack their password.
"The most effective defense against relay attacks is enabling SMB Signing; if it is required, the relay attempt will fail."
📚 Certification: CompTIA PenTest+ (PT0-002)
🔑 What are the Key Concepts of SMB Relay Attack?
- ▸ Targets NTLM authentication challenges, allowing attackers to capture and forward authentication tokens without needing to decrypt or crack the user's actual password.
- ▸ Requires a Man-in-the-Middle position, often achieved through LLMNR or NBT-NS poisoning to redirect traffic from the victim to the attacker's machine.
- ▸ Relies on the absence of SMB Signing, which normally ensures the integrity of the communication and prevents the session from being hijacked by a third party.
- ▸ Facilitates lateral movement by impersonating a victim's identity to execute remote commands or access sensitive shares on other servers within the network.
- ▸ Commonly executed using tools like Responder for interception and Impacket's ntlmrelayx for forwarding the captured authentication to the target server.
🎯 How does SMB Relay Attack appear on the PT0-002 Exam?
You may be asked to identify the correct tool combination for an attack where a tester poisons LLMNR requests and relays them to a target server to gain a remote shell.
A scenario might describe a penetration test where SMB signing is disabled across the domain; you will likely be asked to identify the specific attack vector that leverages this configuration.
Expect questions where you must recommend the most effective remediation for a successful SMB relay attack, specifically focusing on the implementation of required SMB signing across all servers.
❓ Frequently Asked Questions
Does an SMB relay attack require the attacker to crack the password hash?
No. Unlike password cracking or Pass-the-Hash, a relay attack forwards the authentication challenge and response in real-time. The attacker never learns the password but still gains access to the target system.
Why is LLMNR poisoning often used in conjunction with SMB relaying?
LLMNR poisoning tricks a victim's machine into believing the attacker is the intended destination for a network request, forcing the victim to send their NTLM authentication to the attacker's machine first.