jdk8u VS jdk8u_jdk

Would an atomic mutable subclass cache (not sure what it's used for, downcasting?) be unnecessary in a language built around static rather than dynamic dispatch by default, like C/C++/Rust and perhaps Go? Or would it still speed up dynamically dispatched code, but is less practical or worthwhile so it isn't used in practice? (Though Rust's Arc also suffers from atomic contention similar to this blog post, when used across dozens of threads: https://pkolaczk.github.io/server-slower-than-a-laptop/)

Also it's somewhat ironic that the JVM source code (https://github.com/openjdk/jdk8u/blob/jdk8u352-b07/hotspot/s...) says "This code is rarely used, so simplicity is a virtue here" at the site of a bottleneck.

Use the latest JDK (Developer's Kit) or JRE (Runtime Environment) for Java 8, compiled and distributed by AdoptOpenJDK from the official Read-Only source.

The majority of the work on 8u, 11u, 17u releases happens in OpenJDK upstream, in so called JDK Updates Projects, by engineers from the interested JDK vendors. You can get a peek who does this kind of work from the repository histories, for example the most recent 11.0.13 is done by engineers from Red Hat (including yours truly), SAP, Azul, Microsoft, BellSoft, Tencent, Amazon, Alibaba, IBM, ARM, Google.

> whatever it returned would just get inserted as a string into the log output, no big deal.

Once you can inject anything that gets resolved, you have an information disclosure vulnerability unrelated to the RCE.

If I can just DNS resolve any ${env} variable from the JVM, a lot of systems are compromised by just exposing the env or system variables configured for runtime.

Just getting your $AWS_ACCESS_KEY_ID and $AWS_SECRET_ACCESS_KEY env vars can compromise your bucket (sure, that is a really unsafe setup now, but it was almost the standard a few years ago over configuring it explicitly).

So a logging system which will merely resolve a hostname derived from a variable was bad enough to compromise many systems.

The serialization loophole was fixed in a jdk8 update.

https://github.com/openjdk/jdk8u/commit/006e84fc77a582552e71...

But even with that in place, the information disclosure of java System or env properties is bad enough to break actual systems in prod.

> 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.

Out of the box (at least on my text 1.8 JVM): corbaname, dns, iiop, iiopname, ldap, ldaps, rmi

For full details of how this works, use a vulnerable log4j version, log a simple (bad) lookup, and step through with a debugger for a while.

Sources:

* https://github.com/JetBrains/jdk8u_jdk/blob/master/src/share...