Request Smuggling Vulnerability in HAProxy HTTP/3 Parser
CVE-2026-33555
4MEDIUM
Key Information:
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👾 Exploit Exists🟡 Public PoC
What is CVE-2026-33555?
An issue has been identified in HAProxy's HTTP/3 parser prior to version 3.3.6, where the parser fails to ensure that the content length of received bodies corresponds with the previously set content-length. This oversight can lead to desynchronization with backend servers when the stream is terminated unexpectedly via a frame that lacks a payload. Consequently, this flaw can be exploited for request smuggling attacks, potentially allowing an attacker to manipulate traffic between clients and servers.
Affected Version(s)
HAProxy 2.6 < 3.3.6
Exploit Proof of Concept (PoC)
PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.