Log4Shell is a software vulnerability in Apache Log4j 2, a popular Java library for logging error messages in applications. The vulnerability, published as CVE-2021-44228, enables a remote attacker to take control of a device on the internet if the device is running certain versions of Log4j 2.
Attackers can exploit the vulnerability using text messages to control a computer remotely. The Apache Software Foundation, which publishes the Log4j 2 library, gave the vulnerability a CVSS score of 10 out of 10, the highest-level severity score, because of its potential for widespread exploitation and the ease with which malicious attackers can exploit it. While mitigation evolves and the damage unfolds, the fundamentals of the Log4j vulnerability won’t change.