Cyber Security Stories : How a GitHub Bot Was Hijacked to Spread Malicious Code

For weeks, everything seemed normal. Developers across the globe continued using a popular GitHub automation bot, unaware that their trusted tool had been silently compromised. Updates were being pushed, scripts were running, and software projects were progressing as usual—until the reality of a sophisticated cyberattack came to light.

This is exactly what happened to tj-actions, a widely used GitHub repository relied upon by over 23,000 developers. Attackers managed to take control of the automation bot (@tj-actions-bot), injecting malicious code into the repository. Since the bot was responsible for updating the codebase, developers unknowingly pulled in infected code into their projects. For weeks, the malicious code spread undetected, potentially compromising thousands of applications.

🔓 How the Attack Happened

The exact entry point of the attack remains unknown, but security experts have outlined several possible ways the automation bot was compromised:

1️⃣ Leaked API Tokens – If the bot’s credentials were exposed in logs or public repositories, attackers could have stolen and used them to gain access.
2️⃣ Phishing Attack – A deceptive email or a fake GitHub login page may have tricked the bot’s owner into revealing credentials.
3️⃣ Supply Chain Exploit – If the bot relied on outdated or vulnerable dependencies, attackers could have exploited those weaknesses to gain access.

Once inside, the attackers modified the bot’s automation scripts to silently inject malicious code. This meant that every automated update from the bot carried malicious code, making the attack difficult to detect.

🔍 How It Was Detected & Responded To

For weeks, the attack remained under the radar, spreading silently. However, security experts and automated tools eventually picked up on suspicious activity.

👀 Detection

🔹 Security researchers monitoring GitHub noticed irregular script executions and unauthorized changes in commit histories.
🔹 Developers started reporting unexpected behavior in their projects after updating their code.
🔹 Automated security tools flagged anomalies in repository modifications, highlighting unverified changes.

⚠️ Response & Containment

Once the compromise was confirmed, immediate action was taken to limit the damage and contain the threat:
✅ GitHub restricted the repository, preventing further downloads.
✅ The bot’s credentials were revoked, cutting off the attacker's access.
✅ Users were notified to inspect their projects and remove any malicious code.
✅ A full security audit was conducted, identifying all affected systems.

These rapid responses ensured that the malicious code could no longer spread further.

🛠️ Eradication – Removing the Threat

With containment in place, security teams focused on completely eliminating the attacker’s presence:

✅ All compromised versions of the code were removed from the repository.
✅ Developers were provided with guidelines to check and clean their projects.
✅ Security patches and updates were implemented to prevent similar attacks in the future.

🔄 Recovery – Restoring Trust and Operations

After removing the malicious code, the next step was to restore trust in the repository and ensure developers could safely continue their work:

✅ A clean, verified version of the repository was published for safe use.
✅ Developers were advised to re-authenticate their systems and scan for any lingering threats.
✅ Security teams monitored GitHub activity for any further suspicious behavior.

With these measures in place, normal operations resumed, but with stronger security safeguards.

📖 Lessons Learned – What This Attack Taught Us

This incident highlights a major security gap in automation workflows. Attackers exploited privileged automation accounts, showing how critical it is to secure these tools properly.

🔐 Key Takeaways:

1️⃣ Mandatory Multi-Factor Authentication (MFA) – Automation accounts should have MFA enabled to prevent unauthorized access.
2️⃣ Least Privilege Access – Bots should only have the minimum permissions necessary to function.
3️⃣ Routine Security Audits – Credentials, dependencies, and automation tools should be regularly reviewed for vulnerabilities.
4️⃣ Automated Threat Detection – AI-driven monitoring can help catch suspicious activity early.
5️⃣ Cryptographic Signing of Updates – Verifying software updates before execution can prevent unauthorized code injection.

🔍 Incident Investigation Summary (For Analysts)

To understand this breach from an incident response perspective, here’s how it unfolded step by step:

🛑 Detection

✔️ Unusual script executions observed.

✔️ Developers reported unexpected behavior in updated projects.

✔️ Security tools flagged unverified modifications.

⚡ Containment

✔️ GitHub restricted access to the compromised repository.

✔️ The bot’s credentials were revoked, cutting off the attacker's access.

✔️ Developers were alerted and advised to review their projects.

🛠️ Eradication

✔️ Malicious code was removed from the repository.

✔️ Developers were given instructions to clean their codebases.

✔️ Security patches were deployed to prevent a repeat attack.

🔄 Recovery

✔️ A clean, verified version of the repository was released.

✔️ Developers re-authenticated and scanned their systems for threats.

✔️ Security teams continued monitoring for further suspicious activity.

🚀 Lessons Learned & Preventive Controls

✔️ MFA enforcement for automation accounts.

✔️ Restrict automation bots to least privilege access.

✔️ Implement real-time threat monitoring for automated updates.

✔️ Require peer reviews and cryptographic signing for code pushed by bots.

🚀 Final Thought: What Could Have Been Done Better?

This incident raises an important question: How can organizations better secure automation tools and privileged accounts?

✅ Should GitHub enforce stricter security policies for automation accounts?
✅ Could automated security monitoring have detected the attack sooner?
✅ Would cryptographic signing of commits have prevented this breach?

💡 What do you think? What other security measures could have stopped this attack? Drop your thoughts in the comments! 👇