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> Turns out, by including "." in some part of the URL to this remote class, Log4j lets off its guard & simply looks up to that server and dynamically loads the class file.

No it doesn't. That was disabled by default in 2009, and was disabled by default in every release of Java 8 or later: https://github.com/openjdk/jdk8u/commit/006e84fc77a582552e71...

Unless i am mistaken, i don't believe the attack as described by LunaSec actually works against a default-configured JVM released any time in the last decade.




This is my understanding of it as well. While the bug is still bad due to the fact that a JVM instance will connect to the attacker's endpoint, any JVM above 8u121 wouldn't execute the code with Java's default configuration.

It's also mentioned as part of the release notes for 8u121: https://www.oracle.com/java/technologies/javase/8u121-relnot...

Edit: Looking deeper into it; the JDK version used within the POC's GitHub, from the screenshot in that repo, is 8u20, released in 2014.


Aha! It's more complicated than i thought:

https://mbechler.github.io/2021/12/10/PSA_Log4Shell_JNDI_Inj...




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