Threat actors are actively exploiting a critical security flaw in Java logging library Apache Log4j. Log4j is an open-source, Java-based logging utility widely used by enterprise applications and cloud services, meaning many organizations are at risk from threat actors actively exploiting this vulnerability.

The Apache Log4j flaw is a zero-day vulnerability, tracked as CVE-2021-44228, allowing unauthenticated remote code execution and access to servers. Over the weekend, the Apache Software Foundation released a security advisory to address the remote code execution vulnerability affecting Log4j versions 2.0-beta9 to 2.14.1.

Casey Ellis, Founder and CTO at Bugcrowd, a crowdsourced cybersecurity platform, says, “This is a worst-case scenario. The combination of Log4j’s ubiquitous use in software and platforms, the many, many paths available to exploit the vulnerability, the dependencies that will make patching this vulnerability without breaking other things difficult, and the fact that the exploit itself fits into a tweet. The immediate action is to stop what you’re doing as a software shop and enumerate where log4j exists and might exist in your environment and products. It’s the kind of software that can quite easily be there without making its presence obvious, so we expect the tail of exploitability on this vulnerability to be quite long.”

Several agencies, including the Cybersecurity and Infrastructure Agency (CISA), CERT New Zealand and the U.K.’s National Cyber Security Centre (NCSC), have issued warnings, encouraging users and administrators to review and upgrade to Log4j 2.15.0 or apply the recommended mitigations immediately.

CISA Director Jen Easterly, in a statement, said, “CISA is working closely with our public and private sector partners to proactively address a critical vulnerability affecting products containing the log4j software library. This vulnerability, which is being widely exploited by a growing set of threat actors, presents an urgent challenge to network defenders given its broad use. End users will be reliant on their vendors, and the vendor community must immediately identify, mitigate, and patch the wide array of products using this software. Vendors should also be communicating with their customers to ensure end users know that their product contains this vulnerability and should prioritize software updates.”

In addition, CISA has added the vulnerability to the catalog of known exploited vulnerabilities, which asks federal civilian agencies and non-federal partners to urgently patch or remediate this vulnerability. CISA is also recommending asset owners take three additional, immediate steps regarding this vulnerability: 


  1. Enumerate any external-facing devices that have log4j installed. 

  2. Make sure that your security operations center is actioning every single alert on the devices that fall into the category above. 

  3. Install a web application firewall (WAF) with rules that automatically update so that your SOC is able to concentrate on fewer alerts. 

Dor Dali, Director of Information Security at Vulcan Cyber, a provider of SaaS for enterprise cyber risk remediation, says, “Even though it is still early, we’d classify the Log4j vulnerability as very critical, and I would class it in the top-three worst vulnerabilities of 2021. It wouldn’t be a stretch to say that every enterprise organization uses Java, and Log4j is one of the most popular logging frameworks for Java. Connecting the dots, the impact of this vulnerability has the reach and potential to be substantial if mitigation efforts aren’t taken right away. The Log4j vulnerability is relatively easy to exploit, and we’ve already seen verifiable reports that bad actors are actively running campaigns against some of the largest companies in the world. Hopefully, every organization running Java has the ability to secure, configure and manage it. If Java is being used in production systems, IT security teams must prioritize the risk and mitigation campaigns and follow remediation guidelines from the Apache Log4j project as soon as possible.”

Israeli cybersecurity firm Cybereason has also released a fix called “Logout4Shell” that allegedly contains the zero-day vulnerability. “The Cybereason fix appears to be genuine and has the potential to assist security teams. The existing tool’s effectiveness is limited (it does not work for versions prior to 2.10, requires a restart, and the exploit must fire properly in order to be effective), and even when it does run properly, it still leaves the vulnerable code in place,” Ellis explains. “Because of the complexity of regression testing Log4j, I’ve already heard from a number of organizations that are pursuing the workarounds contained in the Cybereason tool as their primary approach. It remains to be seen whether many enterprises choose to exploit the vulnerability itself in order to achieve this, but for the reasons stated above, I would expect at least some to use the tool selectively and situationally.”

Lastly, Ellis adds, “It’s critical to understand that this isn’t a solution - it’s a workaround with a number of limitations. It has intriguing potential as a tool in the toolbox as organizations reduce log4j risk, and if it makes sense for them to use it, one of the primary reasons will be speed to risk reduction.”

CISO of Tanium, Chris Hallenbeck says, “In terms of severity and breadth of impact, this vulnerability certainly is the top one I’ve seen. Ecommerce is a sector that is especially vulnerable to this vulnerability, given how much money flows through ecommerce sites and the terrible timing retailers will now be making emergency changes to their IT environments at their busiest time of the year. To minimize the impact, they should follow the same advice that I would offer organizations from all sectors: identify impacted systems and patch the vulnerability as soon as feasible starting with external-facing IT infrastructure, such as websites, before shifting focus to internal systems. This news is a reminder of the double-edged sword of open source projects. Though open source offers incredible efficiency and development speed, open source does not guarantee that all bugs will be spotted quickly. Open source has cemented itself as a valuable part of enterprise IT — but it's imperative organizations are vigilant in vetting which tools they use including the maintenance of software bill of materials (SBOMs) in order to know when they are impacted. Finally, Log4j highlights the importance of cyber hygiene and asset management. If you have these basics in place before an incident occurs, then you are in a much better position to either prevent any damage being done, or to minimize the impact.”