A vulnerability in the open source Apache logging library Log4j sent system administrators and security professionals scrambling over the weekend. Known as Log4Shell, the flaw is exposing some of the world's most popular applications and services to attack, and the outlook has not improved since the vulnerability came to light on Thursday. If anything, it is now excruciatingly clear that Log4Shell will continue to wreak havoc across the internet for years to come.
Hackers have been exploiting the bug since the beginning of the month, according to researchers from Cisco and Cloudflare. But attacks ramped up dramatically following Apache's disclosure on Thursday. So far, attackers have exploited the flaw to install cryptominers on vulnerable systems, steal system credentials, burrow deeper within compromised networks and steal data, according to a recent report from Microsoft.
The range of impacts is so broad because of the nature of the vulnerability itself. Developers use logging frameworks to keep track of what happens in a given application. To exploit Log4Shell, an attacker only needs to get the system to log a strategically crafted string of code. From there they can load arbitrary code on the targeted server and install malware or launch other attacks. Notably, hackers can introduce the snippet in seemingly benign ways, like by sending the string in an email or setting it as an account username.
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