Recent research has unveiled a sophisticated method to circumvent Web Application Firewall (WAF) protections by leveraging HTTP Parameter Pollution techniques combined with JavaScript injection. This approach exposes significant vulnerabilities in current web security infrastructures, particularly affecting major vendors such as AWS, Google Cloud, Azure, and Cloudflare.
Understanding the Technique
The core of this bypass method lies in exploiting parsing discrepancies between WAF engines and web application frameworks, notably ASP.NET’s parameter handling behavior. ASP.NET processes multiple parameters with the same name by concatenating their values using commas. This behavior can be manipulated to execute Cross-Site Scripting (XSS) attacks that evade traditional security detection mechanisms.
Exploiting ASP.NET Parameter Concatenation
In ASP.NET, when multiple parameters with identical names are encountered, the framework concatenates their values. For instance, a query string like `/?q=1’&q=alert(1)&q=’2` is processed into `1′,alert(1),’2`. When this payload is inserted into a JavaScript context, it becomes valid code: `userInput = ‘1’,alert(1),’2′;`. The comma operator in JavaScript evaluates each expression sequentially, effectively executing the malicious `alert(1)` function while maintaining syntactic validity.
Traditional WAFs often analyze individual parameters without considering how web frameworks parse and concatenate multiple parameter values. This oversight allows attackers to craft payloads that bypass WAF detection by splitting malicious code across multiple parameters.
Research Findings
Security researcher Bruno Mendes conducted tests across 17 different WAF configurations from major vendors, including AWS, Google Cloud, Azure, and Cloudflare. The results were alarming:
– Only 3 out of 17 WAF configurations successfully blocked all manually crafted payloads:
– Google Cloud Armor with ModSecurity rules
– Azure WAF with Microsoft’s Default Rule Set 2.1
– All open-appsec configurations
– Multiple AWS WAF rule sets, including AWS Managed Rules, Cyber Security Cloud rule set, and F5 rule set, were completely bypassed by every payload tested.
– The bypass success rates increased with payload complexity, escalating from 17.6% for simple payloads to 70.6% for sophisticated parameter pollution techniques.
– An automated hackbot achieved a 100% detection evasion rate, successfully finding bypasses for previously resilient WAF configurations.
Implications for Web Security
These findings highlight critical vulnerabilities in current WAF implementations. Organizations investing in WAF solutions may remain susceptible to both sophisticated parameter pollution attacks and surprisingly simple bypass techniques. This underscores the need for continuous evaluation and enhancement of web security measures.
Recommendations
To mitigate the risks associated with this bypass technique, organizations should consider the following actions:
1. Review and Update WAF Configurations: Regularly assess and update WAF rules to address emerging attack vectors, including parameter pollution techniques.
2. Implement Comprehensive Input Validation: Ensure that web applications perform thorough input validation to detect and neutralize malicious payloads before processing.
3. Conduct Regular Security Testing: Engage in routine penetration testing and vulnerability assessments to identify and remediate potential security gaps.
4. Stay Informed on Emerging Threats: Keep abreast of the latest research and developments in web security to proactively defend against new attack methodologies.
By adopting these measures, organizations can enhance their resilience against advanced attack techniques that exploit parsing discrepancies and parameter handling behaviors in web applications.
