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Lesson 8 of 11 · 7 min read

HTTP/2, HTTP/3 and Request Smuggling

Request smuggling happens when a front-end and a back-end parse the boundaries of HTTP/1.1 requests differently, so bytes an attacker sends are treated as the start of the next request on a shared connection. HTTP/2 and HTTP/3 use binary framing that removes that ambiguity, but proxies that accept HTTP/2 and forward HTTP/1.1 reintroduce it, and the new protocols bring their own denial-of-service classes, such as Rapid Reset, which drove record attack rates in 2023. Defences are strict parsing that rejects ambiguous framing, HTTP/2 end to end, per-connection budgets for resets and headers, and care with QUIC's 0-RTT and visibility.

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