Hi Everyone! In this post, I'll explain the Log4j exploit, step-by-step! First, we'll start off by looking at these log files, gathered from a web application running Apache Solr: If you look carefully, there are calls made to a certain parameter in the URL of the web application. Can you spot it? If you look carefully, you'll see that it is /admin/cores. If you're experienced with pen testing, you can probably see where this exploit is going. After doing an nmap scan on the target, we find that port 8983 is open. If you navigate to http://10.10.231.181:8983/, you'll see a page for Apache Solr that indicates that the application is running Log4j. Now, we navigate to http://10.10.231.181:8983/solr/admin/cores. You'll notice that params seems to be included in the log file. The log4j package adds extra logic to logs by "parsing" entries, ultimately to enrich the data -- but may additionally take actions and even evaluate code based off the entry da...
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