Lessons Learned from a Telnet Credential Exploit: Honeypot Insights

In the ever-changing world of cybersecurity, keeping up with attackers means going beyond reactive measures. We need to understand how threats work. Recently, I analyzed a multi-session attack targeting Telnet services using an AWS EC2 honeypot. The findings offer valuable lessons for security professionals.

This article uncovers the methods attackers use, from exploiting weak credentials to staging malware. Let’s explore what happened, why it’s important, and how organizations can learn from it.

On January 16, 2025, a honeypot running on an AWS EC2 instance detected four coordinated attack sessions. The attackers exploited weak Telnet credentials and executed up to 25 commands per session. Their goal? To prepare the environment for further exploitation and botnet integration.

Although network restrictions blocked their payloads, the attack’s methodology highlights the sophistication of botnet campaigns. Reverse engineering the payload revealed its intent to establish persistence and enlist the target into a larger malicious network.

Key Takeaways from the Attack

1. Weak Credentials Still a Problem

Default or easily guessed Telnet passwords allowed attackers to gain access in two sessions. This highlights the ongoing issue of weak password practices, especially in IoT devices where default settings are often left unchanged.

2. Predictable Attack Patterns

Each session followed a clear progression:

• Starting Point: Establishing an interactive shell with commands like sh and enable.
• File Prep: Cleaning directories (e.g., /tmp and /var) to stage malicious payloads.
• Reconnaissance: Scanning writable temporary filesystems (tmpfs) for staging.
• Payload Fetching: Using tools like wget and curl to download files.

Attackers refined their methods based on feedback from the environment, showcasing adaptability.

3. Payload Details

The shell script payload, upon decoding, revealed efforts to identify the target’s system architecture and download additional malware. Its functions included:

• Scanning the network
• Communicating with a command-and-control (C2) server
• Obfuscating activity using encoded payloads

4. Identifying Attack Indicators

Patterns of failed commands and repeated use of utilities like BusyBox offered clear indicators of compromise (IoCs). Additionally, zero-byte file downloads suggested that network restrictions thwarted the attackers’ goals.

Why It Matters

These attacks aren’t one-offs; they’re part of a larger trend targeting IoT and unprotected systems. With tools like Mirai botnets, attackers can launch DDoS attacks, steal data, or move laterally within networks.

By understanding these tactics, organizations can better protect their environments and minimize risks.

How to Defend Against Similar Threats

1. Ditch Telnet for SSH Telnet is outdated and insecure. Replacing it with SSH ensures encrypted communication and stronger authentication.
2. Enforce Strong Passwords Default passwords are an easy target. Use unique, complex passwords and enable multi-factor authentication where possible.
3. Isolate Critical Systems Network segmentation can protect vital infrastructure from potentially vulnerable devices.
4. Monitor Your Network Tools like Zeek or Security Onion can flag suspicious activity. Automate alerts to quickly detect threats.
5. Deploy Honeypots Honeypots like Cowrie provide invaluable insights into attacker methods and offer early warning signs of malicious activity.
6. Keep Software Up to Date Ensure IoT devices and other systems are running the latest firmware and security patches.

Final Thoughts

Staying ahead in cybersecurity means learning from the adversary’s playbook. Honeypots like the one used in this analysis can give us the upper hand by revealing how attackers operate. These insights are crucial for improving defense strategies.

What are your thoughts? Are you using proactive tools like honeypots in your organization? What challenges do you face when securing IoT and cloud environments?

Share your experiences or reach out to discuss further. Together, we can make cybersecurity stronger.