The Terror of Log4j and Why should you be bothered?

Photo by Muhannad Ajjan on Unsplash

Apache Log4j is a java based fast, reliable and flexible logging framework. There are a wide range of frameworks, applications, and tools that leverage Log4j such as Apache Struts2, Apache Solr, Apache Flink, Apache Druid, iCloud, Steam, and Minecraft. The worst-case being not everyone knows whether Log4j is being used in their environment. How many of you really knew elasticsearch uses Log4j? Any organization using Java applications or hardware running Log4j < 2.15 is likely vulnerable.

CVE-2021–44228 (Log4Shell) is an unauthenticated Remote Code Execution(RCE) vulnerability & 0-day exploit which allows an attacker to take over a system that uses Apache Log4j 2.0 to 2.14.1. If successfully exploited, attackers can perform RCE and compromise the affected server leading to a full takeover of the system.

To trigger this vulnerability, all the attacker needs to do is get the app to log a special string. The vulnerability gets triggered if the logged string contains any untrusted strings in any part of the logged data. Guess what can be used to log this string to the system? HTTP headers, Usernames, Email addresses and URLs. Put simply, if you fill a form with the name ${jndi:ldap://} and you’re the owner of it. Try applying for a job in a firm having Log4j with the aforementioned name and the least you could get is a full-time job XD. Have you heard of secret santa? Apparently, this is the perfect gift to bad guys from Santa.

Why does this happen?

Researchers concluded that this is a Java deserialization failure because Log4j makes network requests through the JNDI to an LDAP server and executes any code that is returned. The error is triggered within log messages with the use of the $ {} syntax. And apparently it doesn’t affect the system if JNDI cannot load remote code using LDAP. For insights about how the attack works visit this.


If you’re using Java version less than 1.8 & log4j >= 2.10

  • Setting the system property formatMsgNoLookups: true
  • Set the JVM parameter -Dlog4j2.formatMsgNoLookups=true
  • Elasticsearch using log4j-2.10.x can add -Dlog4j2.formatMsgNoLookups=true to ES_JAVA_OPTS or /etc/elasticsearch/jvm.options
  • Removing JndiLookup class from the classpath

Apache has released Log4j 2.15.0 to address the maximum severity CVE-2021–44228 RCE vulnerability and is recommended to upgrade the vulnerable instances.



index=bro AND http_uri:(\/\$\{jndi\:*)

Network detection using ET Ruleset
tail 10 <

index=* ${jndi:*}

For YARA, visit log4j_rce_detection


Try Hunting for these in your environment.





Breaking the limits ! Privacy Advocate | Developer | Hacker

Love podcasts or audiobooks? Learn on the go with our new app.

Recommended from Medium

{UPDATE} Carnivores Ice Age Hack Free Resources Generator

{UPDATE} Logic Pic+ Gratis Puslespill Hack Free Resources Generator

{UPDATE} Sweet Smash - Merry Christmas Hack Free Resources Generator

Five Ways to Ensure Remote Workers Keep IT Assets Safe


{UPDATE} Ping Song - ear training game Hack Free Resources Generator

You Can Run, But You Can’t Hide — Detecting Process Reimaging Behavior

Create A Crypto Miner Docker Image

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Kai Iyer

Kai Iyer

Breaking the limits ! Privacy Advocate | Developer | Hacker

More from Medium

The Exponential fear of log4j

Walkthrough :

eWPTXv2 Review

Security assesment standards