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    Definitions 3 min read
    Log4Shell logo.
    Log4Shell logo is provided courtesy of Fractional CISO, LLC.

    Log4Shell was a zero-day vulnerability found in Log4j, a popular Java logging framework used on several Java platforms. Log4j, a project of Apache Software Foundation, offers an open-source logging framework for developers for logging purposes, which is a process commonly used by software development teams to record an activity.

    What is Log4Shell?

    Log4Shell is a zero-day vulnerability, as it went unnoticed since 2013. At the time of Log4Shell’s discovery, it had affected hundreds of millions of devices. According to some estimates, it has impacted 3 billion systems globally.

    When was Log4Shell discovered?

    In November 2021, the Log4Shell vulnerability was privately disclosed to Apache Software Foundation by Chen Zhaojun. Zhaojun is a security researcher for Alibaba, which is the largest e-commerce company in China. The vulnerability was disclosed publicly on December 9, 2021, when servers hosting the game Minecraft were attacked.

    The Apache security team set Log4Shell’s severity rating at 10/10 and issued a patch to fix the vulnerability; however, the first patch was not completely successful, requiring subsequent patches to fix Log4 Shell. On December 28, 2021, Apache released the fourth patch to fix the vulnerability.

    How does Log4Shell Work?

    One of the reasons Log4Shell is dangerous is how easy it is to use and how widely used the Log4j library is. Some of the major applications such as VMware and Amazon Web Services (AWS) use Log4j. This widespread use of Log4j makes patching to fix Log4Shell extremely difficult and complex.

    The Log4j library controls how a computer program logs information. This means that when the attackers exploit the Log4Shell vulnerability, they can gain access and control over the string to execute malicious code on the computer program or device. Attackers can even use Log4Shell to take over the servers that house it.

    How does Log4Shell impact businesses?

    As the Log4j library can be used to communicate with other devices within the network, attackers can easily gain control over multiple devices or user accounts on the network. As a result, Log4Shell’s considered an extremely dangerous vulnerability for a business.

    To mitigate the risk, businesses should use scanning tools to check for vulnerabilities in their systems and network and keep up to date with the latest patches. They can also monitor log files and check the network security technology protecting their services. Moreover, they can consider getting cyber insurance to protect against a security breach.