CVE-2026-33555: Haproxy

Medium severity, CVSS 5.8. EPSS: 0.6% chance of exploitation in the next 30 days.

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.

Affected products

• Haproxy Haproxy: from 2.6.0, before 3.3.6 (fixed in 3.3.6)

Published 2026-04-13. Last modified 2026-06-29.