Log4j zero-day flaw: What you need to know and how to protect yourself

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A flaw in Log4j, a Java library for logging error messages in applications, is the most high-profile security vulnerability on the internet right now and comes with a severity score of 10 out of 10.

The library is developed by the open-source Apache Software Foundation and is a key Java-logging framework. Since last week’s alert by CERT New Zealand that CVE-2021-44228, a remote code execution flaw in Log4j, was already being exploited in the wild, warnings have been issued by several national cybersecurity agencies, including the Cybersecurity and Infrastructure Security Agency (CISA) and the UK’s National Cyber Security Centre (NCSC). Internet infrastructure provider Cloudflare said Log4j exploits started on December 1.

What devices and applications are at risk?

Basically any device that’s exposed to the internet is at risk if it’s running Apache Log4J, versions 2.0 to 2.14.1. NCSC notes that Log4j version 2 (Log4j2), the affected version, is included in Apache Struts2, Solr, Druid, Flink, and Swift frameworks.

Mirai, a botnet that targets all manner of internet-connected (IoT) devices, has adopted an exploit for the flaw. Cisco and VMware have released patches for their affected products respectively.


Log4j flaw coverage – what you need to know now


AWS has detailed how the flaw impacts its services and said it is working on patching its services that use Log4j and has released mitigations for services like CloudFront.

Likewise, IBM said it is “actively responding” to the Log4j vulnerability across IBM’s own infrastructure and its products. IBM has confirmed Websphere 8.5 and 9.0 are vulnerable.

Oracle has issued a patch for the flaw, too.

“Due to the severity of this vulnerability and the publication of exploit code on various sites, Oracle strongly recommends that customers apply the updates provided by this Security Alert as soon as possible,” it said.

Necessary actions: Device discovery and patching

CISA’s main advice is to identify internet-facing devices running Log4j and upgrade them to version 2.15.0, or to apply the mitigations provided by vendors “immediately”. But it also recommends setting up alerts for probes or attacks on devices running Log4j.

“To be clear, this vulnerability poses a severe risk,” CISA director Jen Easterly said Sunday. “We will only minimize potential impacts through collaborative efforts between government and the private sector. We urge all organizations to join us in this essential effort and take action.”

Additional steps recommended by CISA include: enumerating any external facing devices with Log4j installed; ensuring the security operations center actions every alert with Log4j installed; and installing a web application firewall (WAF) with rules to focus on Log4j.

AWS has updated its WAF rule set – AWSManagedRulesKnownBadInputsRuleSet AMR – to detect and mitigate Log4j attack attempts and scanning. It also has mitigation options that can be enabled for CloudFront, Application Load Balancer (ALB), API Gateway, and AppSync. It’s also currently updating all Amazon OpenSearch Service to the patched version of Log4j.

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NCSC recommends updating to version 2.15.0 or later, and – where not possible – mitigating the flaw in Log4j 2.10 and later by setting system property “log4j2.formatMsgNoLookups” to “true” or removing the JndiLookup class from the classpath.

Part of the challenge will be identifying software harboring the Log4j vulnerability. The Netherland’s Nationaal Cyber Security Centrum (NCSC) has posted a comprehensive and sourced A-Z list on GitHub of all affected products it is aware are either vulnerable, not vulnerable, are under investigation, or where a fix is available. The list of products illustrates how widespread the vulnerability is, spanning cloud services, developer services, security devices, mapping services, and more.

Vendors with popular products known to be still vulnerable include Atlassian, Amazon, Microsoft Azure, Cisco, Commvault, ESRI, Exact, Fortinet, JetBrains, Nelson, Nutanix, OpenMRS, Oracle, Red Hat, Splunk, Soft, and VMware. The list is even longer when adding products where a patch has been released.

NCCGroup has posted several network-detection rules to detect exploitation attempts and indicators of successful exploitation.

Finally, Microsoft has released its set of indicators of compromise and guidance for preventing attacks on Log4j vulnerability. Examples of the post-exploitation of the flaw that Microsoft has seen include installing coin miners, Cobalt Strike to enable credential theft and lateral movement, and exfiltrating data from compromised systems.

What is Log4j?

Log4J is a widely used Java library for logging error messages in applications. It is used in enterprise software applications, including those custom applications developed in-house by businesses, and forms part of many cloud computing services.

Where is Log4j used?

The Log4j 2 library is used in enterprise Java software and according to the UK’s NCSC is included in Apache frameworks such as Apache Struts2, Apache Solr, Apache Druid, Apache Flink, and Apache Swift.

Which applications are affected by the Log4j flaw?

Because Log4j is so widely used, the vulnerability may impact a very wide range of software and services from many major vendors. According to NCSC an application is vulnerable “if it consumes untrusted user input and passes this to a vulnerable version of the Log4j logging library.”

How widely is the Log4j flaw being exploited?

Security experts have warned that there are hundreds of thousands of attempts by hackers to find vulnerable devices; over 40 percent of corporate networks have been targeted according to one security company.

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