What is Log4j? The Latest Internet Vulnerability [View all]

Log4Shell, an internet vulnerability that affects millions of computers, involves an obscure but nearly ubiquitous piece of software, Log4j. The software is used to record all manner of activities that go on under the hood in a wide range of computer systems.

Jen Easterly, director of the U.S. Cybersecurity & Infrastructure Security Agency, called Log4Shell the most serious vulnerabilityshe’s seen in her career. There have already been hundreds of thousands, perhaps millions, of attempts to exploit the vulnerability.

So what is this humble piece of internet infrastructure, how can hackers exploit it and what kind of mayhem could ensue?

What does Log4j do?

Log4j records events – errors and routine system operations – and communicates diagnostic messages about them to system administrators and users. It’s open-source software provided by the Apache Software Foundation.

A common example of Log4j at work is when you type in or click on a bad web link and get a 404 error message. The web server running the domain of the web link you tried to get to tells you that there’s no such webpage. It also records that event in a log for the server’s system administrators using Log4j.

Similar diagnostic messages are used throughout software applications. For example, in the online game Minecraft, Log4j is used by the server to log activity like total memory used and user commands typed into the console.


https://www.counterpunch.org/2021/12/28/what-is-log4j-the-latest-internet-vulnerability/


https://www.cisa.gov/news/2021/12/22/cisa-fbi-nsa-and-international-partners-issue-advisory-mitigate-apache-log4j