Spring Boot Actuator Bug Worth $55,000+

Spring Boot Actuator Misconfiguration: A Bug Worth $55,000+
Sometimes the most valuable vulnerabilities are hiding in plain sight
One of the best real-world examples is Spring Boot Actuator Misconfiguration - a mistake that has led to bug bounty payouts of $55,000 or more

This issue happens more often than you think, especially when developers leave Actuator endpoints exposed to the public internet.

What Is Spring Boot Actuator and Why It’s Dangerous ​

Spring Boot Actuator provides monitoring and management endpoints for applications.
When misconfigured, these endpoints become a gold mine for bug bounty hunters
Common exposed paths include:

• /actuator
• /actuator/health

If the server responds with 200 OK, hunters immediately start testing other endpoints.

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How Bug Bounty Hunters Find This Vulnerability ​

The first step is always endpoint discovery.
Hunters usually scan for:

• /actuator
• /actuator/info
• /actuator/env
• /actuator/heapdump

Once access is confirmed, the real danger begins.

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Why Heapdump Is the Real Nightmare ​

Developers often try to protect secrets by redacting sensitive values in the /env endpoint.
But here’s the critical mistake
They forget to secure /heapdump.

What Happens with Heapdump?​

The endpoint downloads a file that can be 100MB or more containing live server memory
Inside this file you may find:

• Auth tokens
• API keys
• Database credentials
• Session data
• Sensitive user information

Any secret hidden in /env becomes useless if /heapdump is exposed.

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Example of a Dangerous Request ​

GET /actuator/heapdump HTTP/1.1
Host: vulnerable-site.com

If accessible, the server will return a massive memory dump containing sensitive data

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WAF Bypass Trick Using URL Encoding ​

Sometimes a WAF (Web Application Firewall) blocks direct access to heapdump.
But attackers often try a simple encoding trick.

The Trick ​

Add an encoded # at the end of the path: /actuator/heapdump%23
%23 is the URL-encoded version of #
This can confuse some WAFs and allow the request to pass while the backend still processes it normally.
This bypass works more often than people expect.

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Why This Bug Is So Valuable in Bug Bounty ​

This vulnerability can lead to:

• Full account takeover
• Internal system access
• Cloud credential leaks
• Complete infrastructure compromise

That’s why companies pay five-figure rewards for finding it

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Key Takeaways for Pentesters and Bug Hunters ​

If you’re doing pentesting or bug bounty hunting:

• Don’t stop at health checks
• Test all Actuator endpoints
• Always try URL encoding to bypass WAF rules
• Treat heapdump as critical severity

One exposed endpoint can mean full compromise.

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Final Lesson ​

The vulnerability isn’t advanced hacking. It’s bad configuration.
Secure your Actuator endpoints, restrict access, and never expose them to the public internet
Happy hacking - ethically