Description
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
References7
- github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0db… Patch
- r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smug… ExploitThird Party Advisory
- r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smug… ExploitThird Party Advisory
- www.haproxy.com/documentation/haproxy-aloha/changelog/ Release Notes
- www.haproxy.org Product
- www.mail-archive.com/[email protected]/msg46752.html Release Notes
- lists.debian.org/debian-lts-announce/2026/10/msg00036.html
Metrics
- CVSS 3.1
-
5.8
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - EPSS — exploit probability
- 0% percentile: 25 · as of 12 November 2026
- CWE
- CWE-130
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.