CVE-2026-33555

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.

• CWE-130

• https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84Patch
• https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.htmlExploit, Third Party Advisory
• https://www.haproxy.com/documentation/haproxy-aloha/changelog/Release Notes
• https://www.haproxy.orgProduct
• https://www.mail-archive.com/haproxy@formilux.org/msg46752.htmlRelease Notes
• https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.htmlExploit, Third Party Advisory

Published

Apr 13, 2026

Last Modified

Jun 29, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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