Log4j 2: A Week Look Back

Original Entry by : Michael Morris

Do you know if you have been attacked?

By Michael Morris, Director of Global Business Development, Endace

Michael Morris, Director of Global Business Development, Endace

Log4J 2 - how can you see if you've been attacked?Many organizations have been scrambling this week to search their networks for instances of any use of Log4j 2 libraries and quickly patch applications, systems, appliances, or devices that might be using them. Lots of cycles are being spent reaching out to equipment and software vendors trying to determine if their systems or applications are potentially impacted and applying fixes and updates to stop potential compromises. The primary response for most security teams has been to apply patches and plug the holes.

But what exactly is the threat?  Apache Log4j 2 Java library is vulnerable to a remote code execution vulnerability (CVE-2021-44228) known as Log4Shell. This gives remote unauthenticated attackers the ability to execute arbitrary code loaded from a malicious server with the privileges of the Log4j 2 process.

It is nicely illustrated in this diagram from the Swiss Government Computer Emergency Response Team:


Log4J2 - JNDI attack process
(from: https://www.govcert.ch/blog/zero-day-exploit-targeting-popular-java-library-log4j/)

Any system with this vulnerability is now an entry point for the seeding or running of remote code execution that could then conduct any number of other nefarious activities.

I have been reading numerous articles and attending various seminars from threat intel teams such as Palo Alto Network Unit 42, that discuss the risk, scale, and severity of the potential risks to organizations from this zero-day threat. There are several key takeaways I have learned.

First, because of the prevalence of this vulnerability, literally millions of systems are at risk. Second, because of the scale of attacks leveraging this vulnerability there have already been several compromises and ransomware attacks. However, a lot of the current threat actor activity to this point appears to be reconnaissance and planting of additional malware that can be used later after threat actors have obtained initial access to a network and systems on it.

Our technology partner, KeySight Technology, has been tracking honeypot activity which shows huge numbers of exploitation attempts – demonstrating how many threat actors are scanning the internet looking for vulnerable systems.

Industry-wide there are already a huge number of bots scanning the internet simply looking for openings. Key advice from threat intel teams is to immediately isolate any impacted servers as they are truly open backdoors to the rest of your infrastructure. There are numerous tools out there to scan your environment for Log4j 2 use.

Anywhere that Log4j 2 is found you need to isolate and investigate for any potential compromises. It’s essential to put in place policies, rules, and filter protections to monitor outbound egress of traffic to unknown IP addresses. Apply filters and pay extra attention to common traffic protocols like LDAP, LDAPS, RMI, DNS as these are key protocols being leveraged for lateral movement and reconnaissance. Look for anomalous or unexpected traffic to and from potentially compromised systems if you are unable to isolate them.

Of course, you should also ensure your IDS’s or firewalls have updated rule sets for Log4j 2 so that you can block or detect any future attempts to infect your network. This needs to be done quickly so you can get on with the job of reviewing any damage that may have been done.

If you’re collecting network metadata on a SIEM such as Splunk or Elastic, the first place to start looking would be to search all http transactions for strings including JNDI calls. Our partner, Splunk, published a blog on how to do this here:


Once you have identified any JNDI calls, it’s critical to review the recorded network packet data to determine if any outgoing connections were made from potentially compromised servers.

EndaceProbes can capture weeks or months of packet data, allowing you to quickly review potential threats that may have occurred prior to the public announcement of the Log4j 2 vulnerability. Chris Greer published a very useful YouTube video of how to use Wireshark to identify and analyze a Log4j2 attack. Well worth watching:

Once you have identified connections that contain the JNDI string you can quickly examine any the subsequent outgoing connections from the affected host to see if successful contact was made with the malicious LDAP server, downloading java malware to infect your server. Knowing whether this step did or did not happen will save your team many days of incident response and allow them to focus on the servers that have been compromised.

Good luck with the Log4j 2 threat hunting! To learn more about how cost effective and simple it can be to have an always-on network packet capture platform integrated with the rest of your security tools to help you search for Log4J 2 and other zero-day attacks go to www.endace.com.