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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:

Rule ID Description Default Action
100514 (legacy WAF)
6b1cc72dff9746469d4695a474430f12 (new WAF)
Log4J Headers BLOCK
100515 (legacy WAF)
0c054d4e4dd5455c9ff8f01efe5abb10 (new WAF)
Log4J Body BLOCK
100516 (legacy WAF)
5f6744fa026a4638bda5b3d7d5e015dd (new WAF)
Log4J URL BLOCK

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:

Rule ID Description Default Action
100517 (legacy WAF)
2c5413e155db4365befe0df160ba67d7 (new WAF)
Log4J Advanced URI, Headers DISABLED

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 <= 2.14.1 JNDI features used in configuration, log messages, and parameters can be exploited by an attacker to perform remote code execution. Specifically, an attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled.

In addition, the previous mitigations for CVE-2021-22448 as seen in version 2.15.0 were not adequate to protect against CVE-2021-45046.