log4shell-tools VS aegis4j

I'm seeing this as well. While the amount of traffic has certainly decreased compared to the first couple of days after the CVE was announced, https://log4shell.tools is still being used by people every day.

e.g. from log4j. Taken from https://log4shell.tools/

I run tests with https://log4shell.tools, and it seems I'm vulnerable on client side, but my server is safe, which makes sense as I compiled the .jar 2 weeks ago with BuildTools as indicated here https://www.spigotmc.org/threads/spigot-security-releases-%E2%80%94-1-8-8%E2%80%931-18.537204/

You're right, but this has always been the trade off with tools like this. You put some trust in the tool's authors and gain some insight in return. Remember the services that tested for Heartbleed (e.g. https://filippo.io/Heartbleed/)? Fairly similar trade-off, but still these tools were widely used.

If you really don't trust me and have some technical know-how, you can self host the service. It's open source: https://github.com/alexbakker/log4shell-tools.

I can't say I'm feeling the same. Still lots of people testing over at https://log4shell.tools almost a week after this vulnerability became widely known. Plenty of people still discovering they're vulnerable as well. I think it's likely that these are just the people who know they're using log4j. If you're running a black box product from a vendor you'll have no clue you're vulnerable until it's too late.

I have a feeling this vulnerability is going to be with us for years. Shameless plug: I built a tool that assists in detecting whether you're vulnerable to this or the previous CVE: https://log4shell.tools. Just enter the JNDI URI it gives you anywhere you suspect it ends up causing a message lookup in log4j. If log4j does so much as a DNS lookup, this tool will tell you about it.

Done! https://github.com/alexbakker/log4shell-tools

The guys at Oracle have made this point on this forum quite often, but it never really hit home for me personally until the recent log4j vulnerability made me more interested in the topic and the available mitigation options (see https://github.com/gredler/aegis4j/).

If you've been impacted by these log4j vulnerabilities, have a look at aegis4j, a Java agent that completely disables platform features you don't use, before an attacker uses them against you (including e.g. JNDI and Java serialization).

https://github.com/gredler/aegis4j/

Yep, this is why strategically patching InitialContext when the class is initially loaded will completely disable JNDI (and mitigate future JNDI-based exploits).

The recent log4j vulnerability really piqued my interest, and I've spent the last few evenings working on a proof of concept Java agent that could mitigate similar vulnerabilities in the future, for applications that are able to completely forego platform features like JNDI, serialization or native process execution.

Link to the project: https://github.com/gredler/aegis4j

It's not a lot of code, but it uses parts of the platform that I think are a bit unusual for most devs, so it was quite interesting to implement. Happy to discuss details, ideas, and concerns.

One idea for a possible improvement is to make the feature block list adaptive, i.e. watch what the application uses in the first few minutes of execution, and then shut down all unused "dangerous" features for the remaining lifetime of the VM. Not sure how reliable this would be though, especially for services which have background jobs that might only run once a day.