XSS Filters: Beating Length Limits Using Spanned Payloads - Port Swigger
Summary: PortSwigger Research describes a technique for beating input length limits by spanning an XSS payload across multiple user-controllable fields that are reflected on the same returned page. In the Hackxor example, four input fields each capped at 10 characters are chained using JavaScript comments to comment out the intervening source code, allowing a payload ending in a 10-byte closing script tag to execute.
What's compelling: A 10-character limit on each field looks like a control, but four reflected fields on one page gave the researcher enough room to assemble a working script - so per-field length limits do not bound what an attacker can build across a single response.
Read the original at PortSwigger Research ↗
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