This tweet highlights an interesting bypass technique for context-aware Web Application Firewalls (WAFs) that struggle with HTML attribute encoding. Essentially, these WAFs try to detect attacks by looking at HTML attributes enclosed in quotes, but they may not correctly handle percent-encoded quotes like %22. When an attacker uses %22 instead of actual quotes, the WAF interprets the attribute as quoted, while the application receiving the request sees it as unquoted. This difference in parsing behavior creates an opportunity for bypassing the WAF's security filters. Such bypasses can apply to various vulnerability types, including Cross-Site Scripting (XSS), where malicious payloads are injected through HTML attributes. The key insight here is exploiting how encoding tricks can deceive security mechanisms, showing the importance of proper and thorough input normalization and decoding in WAF implementations.
For more insights, check out the original tweet here: https://twitter.com/ctbbpodcast/status/1958204940184129914. And don’t forget to follow @ctbbpodcast for more exciting updates in the world of cybersecurity.