EUVD-2026-21997
GHSA-5mp8-rq5m-pj7m
CVSS VectorNVD
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
Lifecycle Timeline
2DescriptionNVD
An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.
AnalysisAI
HAProxy versions 2.6 through 3.3.5 fail to validate that received HTTP/3 message body lengths match the announced Content-Length header when streams close via empty-payload frames, enabling request smuggling and backend desynchronization attacks. An unauthenticated remote attacker can exploit this via network-level HTTP/3 traffic to cause integrity violations (integrity impact rated low by CVSS), though practical exploitation requires high attack complexity. …
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External POC / Exploit Code
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