WAFFLED: New Technique Targets Web Application Firewall Weaknesses

Cybersecurity researchers at Northeastern University and Dartmouth College have unveiled a groundbreaking attack technique that exploits fundamental parsing discrepancies in Web Application Firewalls (WAFs), potentially compromising the security of millions of websites worldwide.

The research, dubbed “WAFFLED” (Web Application Firewall Fuzzing through Language Exploitation and Discrepancy), demonstrates how attackers can bypass five major WAF platforms.

Including AWS WAF, Azure WAF, Google Cloud Armor, Cloudflare, and ModSecurity—by exploiting inconsistencies in how these security systems parse HTTP requests compared to web application frameworks.

Revolutionary Attack Methodology

Led by Seyed Ali Akhavani from Northeastern University, the research team identified 1,207 unique bypass techniques across popular web frameworks including Flask, Laravel, FastAPI, Gin, Express, and Spring Boot.

Unlike traditional WAF evasion methods that rely on obfuscating malicious payloads, WAFFLED keeps attack payloads intact while manipulating specific content elements to confuse WAF parsing mechanisms.

The technique targets three widely used content types: multipart/form-data, application/json, and application/xml.

By exploiting features such as boundary definitions in multipart data, namespace variations in XML, and field wrapper manipulations in JSON, attackers can cause WAFs to misinterpret requests while web applications correctly process and execute the malicious code.

The researchers’ analysis of 100 real-world websites revealed that over 90% accept both form-encoded and multipart data interchangeably, highlighting the broad applicability of these bypass techniques.

This finding suggests that the vulnerabilities could affect a significant portion of web applications currently protected by WAFs.

The study classified bypasses into 24 distinct categories, with JSON-based attacks accounting for 557 bypasses, multipart attacks for 351 bypasses, and XML-based attacks for 299 bypasses.

Each category exploits different parsing inconsistencies, from boundary delimiter manipulation to content-type header modifications.

Major technology vendors have acknowledged the vulnerabilities and are implementing fixes. Google Cloud Armor classified the report as a “Tier 1, Priority 1, Severity 1” vulnerability and awarded the researchers a bug bounty.

Cloudflare confirmed the bypasses and stated they are working on remediation, while Microsoft Azure acknowledged the issues and is transitioning to an enhanced ruleset.

To address these vulnerabilities, the research team developed HTTP-Normalizer, a proxy tool that enforces strict RFC standards compliance.

The tool demonstrated 100% effectiveness in blocking all identified bypass attempts by normalizing HTTP requests before they reach WAFs.

This research exposes critical weaknesses in how WAFs parse and interpret HTTP traffic, potentially forcing a fundamental rethink of web application security architectures.

The findings emphasize the need for improved parsing consistency across security platforms and highlight the ongoing cat-and-mouse game between attackers and defenders in cybersecurity.

The complete research findings and mitigation tools have been made publicly available to help organizations better protect their web applications against these sophisticated bypass techniques.

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