This tweet demonstrates a bypass of the CloudFlare WAF (Web Application Firewall) for an XSS (Cross-Site Scripting) vulnerability. The payload consists of an SVG tag with an onload event that triggers an alert. When the payload is >\u003csvg onload=alert()> it is blocked by the WAF, but when a null byte %00 is added immediately after the tag (>\u003csvg onload=alert()>%00), the alert pops up, indicating that the WAF filtering has been bypassed. This bypass is significant because it shows that injecting a null byte can confuse the WAF's detection mechanisms, allowing malicious scripts to execute despite the protections in place. Such bypass techniques are important for security researchers and developers to understand so they can improve WAF rules and prevent exploitation of XSS vulnerabilities.
For more insights, check out the original tweet here: https://twitter.com/Psuedo0x00/status/1964030554749489223. And don’t forget to follow @Psuedo0x00 for more exciting updates in the world of cybersecurity.