QwikSec

Security Database

CVE

CWE

Training

CVE-2026-33555

Published: Apr 13, 2026

Modified: Apr 22, 2026

PUBLISHED

CVSS v3.1

4.0

MEDIUM

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.

Vendor	Product	Versions
HAProxy	HAProxy	affected `2.6 - < 3.3.6`

Weaknesses (CWE)

CVSS v3.1 Details

CVSS v3.1 Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

None

Integrity

Low

Availability

None

References

https://www.haproxy.org

https://www.haproxy.com/documentation/haproxy-aloha/changelog/

https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84

https://www.mail-archive.com/[email protected]/msg46752.html

https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html

Security Training

Train your team to recognize and prevent security threats with our comprehensive security awareness program.

Vulnerability Scanning

Discover vulnerabilities in your applications and infrastructure before attackers do.