Shortly before the December holidays, a vulnerability in the ubiquitous Log4J library arrived like the Grinch, Scrooge, and Krampus rolled into one monstrous bundle of Christmas misery. Log4J maintainers went to work patching the exploit, and security teams scrambled to protect millions of exposed applications before they got owned. At Cribl, we put together multiple resources to help security teams detect and prevent the Log4J vulnerability using LogStream.

You have probably heard of Log4Shell, the security vulnerability that has ‘earned’ itself an NIST rank of 10: In this post I will show a really basic example of how this vulnerability actually works. I will walk you through some basic usage of the Log4J library and then show how some fairly basic inputs into this library can cause truly unexpected, and potentially disastrous, outcomes.

The high risk associated with newly discovered vulnerabilities in the highly popular Apache Log4j library – CVE-2021-44228 (also known as Log4Shell) and CVE-2021-45046 – has led to a security frenzy of unusual scale and urgency. Developers and security teams are pressed to investigate the impact of Log4j vulnerabilities on their software, revealing multiple technical challenges in the process.

The Log4J library is one of the most widely-used logging libraries for Java code. On the 24th of November 2021, Alibaba’s Cloud Security Team found a vulnerability in the Log4J, also known as log4shell, framework that provides attackers with a simple way to run arbitrary code on any machine that uses a vulnerable version of the Log4J. This vulnerability was publicly disclosed on the 9th of December 2021.

The discovery of the Log4Shell vulnerability in the ubiquitous Apache Log4j package is a singular event in terms of both its impact and severity. Over 1 million attack attempts exploiting the Log4Shell vulnerability were detected within days after it was exposed, and it may take years before we see its full impact.

If you have access to the internet, it’s likely that you have already heard of the critical vulnerability in the Log4j library. A zero-day vulnerability in the Java library Log4j, with the assigned CVE code of CVE-2021-44228, has been disclosed by Chen Zhaojun, a security researcher in the Alibaba Cloud Security team. It’s got people worried—and with good reason.

At many organizations, the surprise discovery that the widely used Apache log4j open source software has harbored a longtime critical vulnerability was as if Scrooge and the Grinch had teamed up for the biggest holiday heist of all. Incident response teams across the globe have scrambled to remediate thousands, if not millions of applications. “For cybercriminals this is Christmas come early,” explained Theresa Payton, former White House CIO and current CEO of Fortalice Solutions.

VMware has published a detailed analysis of the Log4Shell exploitation, explaining how VMware security products are helping in multiple ways to detect and contain the exploit. Source: Swiss Government Computer Emergency Response Team.

The internet has been ablaze since the announcement of Log4Shell, the nickname for CVE-2021-44228, an arbitrary remote code execution vulnerability in the Java logging utility Log4j. So far two additional vulnerabilities ( CVE 2021-45046, CVE-2021-45105) have now been identified. The code has been vulnerable since 2013 and millions of hosts and services are affected.