CVE-2021-44228 (Log4Shell or LogJam) is a recently discovered zero-day vulnerability in the ubiquitous Apache Log4j Java-based logging library. It was reported by the Alibaba Cloud Security team as an unauthenticated RCE vulnerability in Log4j 2.0-beta9 up to 2.14.1 and could allow a complete system takeover on vulnerable systems. The bug has received the maximum CVSS score of 10, reflecting its importance and ease of exploitation.
This logging library is widely used in enterprise applications from Apple, Twitter, Amazon, Tesla, CloudFlare, and products including Apache Struts2, Apache Solr, Apache Druid, and Apache Flink for its rich feature set and ability to flexibly record log information. Even Ghidra, a popular reverse engineering tool from NSA, is vulnerable to this bug. Attackers can use the feature that is used to write error logs to construct special data request packets through this vulnerability and ultimately trigger the remote code execution.
Threat actors were observed scanning the Internet for servers vulnerable to this unauthenticated RCE after the first POC exploit was published on GitHub. There are also many reports of Log4Shell abuse in the wild, where threat actors are pushing different types of malware, such as Mirai and Tsunami botnets, Cobalt Strike, and Cryptominers.