# Course 38 - Web Security Known Web Attacks | Episode 3: RFD, Mutation XSS, and RPO

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Podcast: [CyberCode Academy](https://stenobird.com/podcast/cybercode-academy-7578615)
Published: 2026-07-04T06:00:02+00:00
Episode link: https://www.spreaker.com/episode/course-38-web-security-known-web-attacks-episode-3-rfd-mutation-xss-and-rpo--72711731
Audio file: https://dts.podtrac.com/redirect.mp3/api.spreaker.com/download/episode/72711731/weaponizing_browser_logic_for_web_attacks.mp3
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Duration seconds: 987

## Resource

In this lesson, you’ll learn about: Reflected File Download (RFD), Mutation XSS (mXSS), and Relative Path Overwrite (RPO) XSS1. Reflected File Download (RFD)🔹 Definition: A vulnerability where user input is reflected into a response that the browser treats as a downloadable file 🔹 How it works (high-level): Attacker crafts a URL Server reflects input into response Browser downloads it as a file (e.g., .bat, .cmd) 👉 Key Insight The attack relies more on social engineering than pure technical exploitation2. Why RFD is Dangerous🔹 Core risk: User executes a malicious file thinking it’s legitimate 🔹 Attack characteristics: File appears trusted (same domain) Filename can be manipulated Content may contain system commands 👉 Key Insight Trust in the source (domain) is what makes this attack effective3. Advanced RFD Scenario🔹 More dangerous variant: Malicious script modifies browser behavior 🔹 Example impact: Weakens browser protections Enables further data access 👉 Key Insight RFD can act as an entry point for deeper compromise4. Mutation XSS (mXSS)🔹 Definition: A type of XSS where safe input becomes dangerous after browser processing 🔹 Root cause: Browser mutates (transforms) HTML internally 👉 Key Insight The payload is not dangerous initially—it becomes dangerous after parsing5. How mXSS HappensUsing JavaScript:🔹 Scenario: Application inserts sanitized input into DOM Browser reinterprets it via innerHTML Encoded content becomes executable 👉 Key Insight Security filters can fail due to DOM re-parsing behavior6. Why mXSS Is Tricky🔹 Challenges: Payload looks harmless Bypasses traditional filters Depends on browser quirks 👉 Key Insight mXSS exploits differences between sanitization and rendering7. Relative Path Overwrite (RPO) XSS🔹 Definition: Exploits how browsers resolve relat…

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