Inconsistent interpretation of HTTP requests in HAProxy - CVE-2026-33555
Published: April 15, 2026
Vulnerability identifier: #VU126147
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-33555
CWE-ID: CWE-444
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: HAProxy
Affected software:
HAProxy
HAProxy
Detailed vulnerability description
The vulnerability allows a remote attacker to perform HTTP request smuggling attacks.
The vulnerability exists due to improper validation of HTTP/3 requests. A remote attacker can send a specially crafted HTTP/3 request to the server and smuggle arbitrary HTTP headers.
Successful exploitation of vulnerability may allow an attacker to poison HTTP cache and perform phishing attacks.
How to mitigate CVE-2026-33555
Install updates from vendor's website.