CVE-2021-44228 – Log4j RCE 0-day mitigation

CVE-2021-44228 - Log4j RCE 0-day mitigation

A zero-day exploit affecting the popular Apache Log4j utility (CVE-2021-44228) was made public on December 9, 2021 that results in remote code execution (RCE).

This vulnerability is actively being exploited and anyone using Log4j should update to version 2.15.0 as soon as possible. The latest version can already be found on the Log4j download page.

If updating to the latest version is not possible, customers can also mitigate exploit attempts by setting the system property “log4j2.formatMsgNoLookups” to “true”; or by removing the JndiLookup class from the classpath. Java release 8u121 also protects against this remote code execution vector.

Customers using the Cloudflare WAF can also leverage three newly deployed rules to help mitigate any exploit attempts:

Rule ID
Default Action

100514 (legacy WAF)
6b1cc72dff9746469d4695a474430f12 (new WAF)
Log4j Headers

100515 (legacy WAF)
0c054d4e4dd5455c9ff8f01efe5abb10 (new WAF)
Log4j Body

100516 (legacy WAF)
5f6744fa026a4638bda5b3d7d5e015dd (new WAF)
Log4j URL

The mitigation has been split across three rules inspecting HTTP headers, body and URL respectively.

Due to the risk of false positives, customers should immediately review Firewall Event logs and switch the Log4j Body and URL rules to BLOCK if none are found. The rule inspecting HTTP headers has been directly deployed with a default action of BLOCK to all WAF customers.

We are continuing to monitor the situation and will update any WAF managed rules accordingly.

More details on the vulnerability can be found on the official Log4j security page.

Who is affected

Log4j is a powerful Java based logging library maintained by the Apache Software Foundation.

In all Log4j versions >= 2.0-beta9 and

Source:: CloudFlare