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.
Exploitability
AV:NAC:HPR:NUI:NScope
S:CImpact
C:NI:LA:N4/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:NOther