The 'formatMsgNoLookups' property was added in version 2.10.0, per the JIRA Issue LOG4J2-2109 [1] that proposed it. Therefore the 'formatMsgNoLookups=true' mitigation strategy is available in version 2.10.0 and higher, but is no longer necessary with version 2.15.0, because it then becomes the default behavior [2][3].
If you are using a version older than 2.10.0 and cannot upgrade, your mitigation choices are:
- Substitute a non-vulnerable or empty implementation of the class org.apache.logging.log4j.core.lookup.JndiLookup, in a way that your classloader uses your replacement instead of the vulnerable version of the class. Refer to your application's or stack's classloading documentation to understand this behavior.
Confirming that this is correct: the {nolookups} option was added in v2.7 as a result of LOG4J2-905, so this mitigation is not available on versions prior to 2.7. Corroborating sources:
Checking on the viability of the classloading-based mitigations now across the versions. It seems that LOG4J-1051 was raised [6] to make the class instantiator more tolerant of missing classes, and the resulting changes were released in v2.4 and v2.7. Will check how earlier versions behave in this case.
If you are using a version older than 2.10.0 and cannot upgrade, your mitigation choices are:
- Modify every logging pattern layout to say %m{nolookups} instead of %m in your logging config files, see details at https://issues.apache.org/jira/browse/LOG4J2-2109
or
- Substitute a non-vulnerable or empty implementation of the class org.apache.logging.log4j.core.lookup.JndiLookup, in a way that your classloader uses your replacement instead of the vulnerable version of the class. Refer to your application's or stack's classloading documentation to understand this behavior.
[1] https://issues.apache.org/jira/browse/LOG4J2-2109 [2] https://github.com/apache/logging-log4j2/pull/607/files [3] https://issues.apache.org/jira/browse/LOG4J2-3198