This tweet talks about a WAF bypass involving the famous Log4Shell vulnerability, which is a Remote Code Execution (RCE) type exploit. The bypass technique uses very complex obfuscation in the attack payload. Obfuscation is a method to disguise the attack code to avoid detection. This is especially effective against Web Application Firewalls (WAFs) that rely on regular expressions (regex) for detecting attacks. Regex-based WAFs look for specific patterns in web traffic, but complex obfuscation can evade these pattern matches, allowing the attack to get through. This sample was captured through a honeypot, a trap set up to detect attacks in the wild. The implementation mentioned in the tweet suggests there are ways to bypass many regex-based WAFs with such obfuscated Log4Shell attack payloads. In summary, attackers are improving their evasion techniques against WAFs, making traditional regex detection less effective against critical vulnerabilities like Log4Shell RCE.
Check out the original tweet here: https://twitter.com/pyn3rd/status/1999451476897464382