A sophisticated method to bypass Web Application Firewall (WAF)<\/a> protections using HTTP Parameter Pollution techniques combined with JavaScript injection.\u00a0<\/p>\n The research, conducted by Bruno Mendes across 17 different WAF configurations from major vendors including AWS, Google Cloud, Azure, and Cloudflare, revealed alarming vulnerabilities in the current web security infrastructure.\u00a0<\/p>\n The technique exploits fundamental parsing differences between WAF engines and web application frameworks, particularly ASP.NET\u2019s parameter handling behavior, to execute Cross-Site Scripting (XSS)<\/a> attacks that evade traditional security detection mechanisms.<\/p>\n The breakthrough technique leverages ASP.NET\u2019s specific behavior when processing duplicate HTTP parameters.\u00a0<\/p>\n When ASP.NET encounters multiple parameters with the same name through its HttpUtility.ParseQueryString() method, it concatenates their values using commas.\u00a0<\/p>\n This behavior creates an opportunity for sophisticated bypasses when combined with JavaScript\u2019s comma operator syntax.<\/p>\n The researchers at Ethiack demonstrated how a seemingly benign query string like \/?q=1\u2019&q=alert(1)&q=\u20192 gets processed by ASP.NET into the concatenated form 1\u2032,alert(1),\u20192.\u00a0<\/p>\n When this payload is inserted into a JavaScript context, such as userInput = \u2018USER_CONTROLLED_DATA\u2019;, it becomes valid JavaScript code: userInput = \u20181\u2019,alert(1),\u20192\u2032;.\u00a0<\/p>\n The comma operator in JavaScript evaluates each expression sequentially, effectively executing the malicious alert(1) function while maintaining syntactic validity.<\/p>\n Traditional WAFs struggle to detect this technique because they typically analyze individual parameters rather than understanding how web frameworks parse and concatenate multiple parameter values.\u00a0<\/p>\n Bruno Mendes tested<\/a> three increasingly sophisticated payloads, ranging from simple injection attempts like q=\u2019;alert(1),\u2019 to complex parameter pollution payloads using newlines and variable assignments such as q=1\u2019%0aasd=window&q=def=\u201dal\u201d+\u201dert\u201d&q=asd[def](1)+\u2019.<\/p>\n The testing results exposed significant gaps in current WAF protection mechanisms.\u00a0<\/p>\n Only three out of 17 tested configurations successfully blocked all manually crafted payloads: Google Cloud Armor with ModSecurity rules, Azure WAF with Microsoft\u2019s Default Rule Set 2.1, and all open-appsec configurations.\u00a0<\/p>\n Notably, 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.<\/p>\n The bypass success rates increased dramatically with payload complexity, escalating from 17.6% for simple payloads to 70.6% for sophisticated parameter pollution techniques.\u00a0<\/p>\n Even more concerning, the researchers\u2019 automated \u201chackbot\u201d achieved a 100% detection evasion rate, successfully finding bypasses for previously resilient WAF configurations.\u00a0<\/p>\n For instance, the hackbot discovered that Azure WAF could be bypassed using a simple payload test\\\u2019;alert(1);\/\/ that exploits parsing discrepancies in escaped character handling.<\/p>\n The research highlighted a critical security paradox: organizations investing in expensive WAF solutions may remain vulnerable to both sophisticated parameter pollution attacks and surprisingly simple bypass techniques.\u00a0<\/p>\n The findings demonstrate that signature-based WAFs are particularly susceptible to these attacks, while machine learning-based solutions show better detection capabilities but still contain exploitable vulnerabilities.\u00a0<\/p>\n This research underscores the fundamental limitation that WAFs cannot fully simulate application parsing behavior, creating differential vulnerabilities that skilled attackers can exploit.<\/p>\n The post WAFs protection Bypassed to Execute XSS Payloads Using JS Injection with Parameter Pollution<\/a> appeared first on Cyber Security News<\/a>.<\/p>\n<\/div>\nKey Takeaways<\/mark><\/strong>
1. Splitting XSS payloads across multiple HTTP parameters defeats WAF detection.
2. Only 3 out of 17 major WAF configurations blocked sophisticated parameter pollution attacks.
3. AI hackbot achieved 100% bypass success, finding simple exploits in seconds.<\/pre>\nExploiting ASP.NET Parameter Concatenation\u00a0<\/strong><\/h2>\n
WAF Vulnerabilities Discovered<\/strong><\/h2>\n
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