Protection against CVE-2021-45046, the additional Log4j RCE vulnerability

Hot on the heels of CVE-2021-44228 a second Log4J CVE has been filed CVE-2021-45046. The rules that we previously released for CVE-2021-44228 give the same level of protection for this new CVE.

This vulnerability is actively being exploited and anyone using Log4J should update to version 2.16.0 as soon as possible, even if you have previously updated to 2.15.0. The latest version can be found on the Log4J download page.

Customers using the Cloudflare WAF have three rules to help mitigate any exploit attempts:

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

In addition to the above rules we have also released a fourth rule that will protect against a much wider range of attacks at the cost of a higher false positive rate. For that reason we have made it available but not set it to BLOCK by default:

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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:

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. Continue reading