CVE-2026-33555

EUVD-2026-21997
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.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
4 MEDIUM
NETWORK
HIGH
NONE
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: 21.69%
Affected Products (NVD)
VendorProductVersion
haproxyhaproxy
2.6.0 ≤
𝑥
< 3.3.6
𝑥
= Vulnerable software versions
Debian logo
Debian Releases
Debian Product
Codename
haproxy
bookworm
ignored
bookworm (security)
vulnerable
bullseye
2.2.9-2+deb11u6
fixed
bullseye (security)
2.2.9-2+deb11u7
fixed
forky
3.2.22-1
fixed
sid
3.2.22-1
fixed
trixie
3.0.11-1+deb13u3
fixed
trixie (security)
3.0.11-1+deb13u3
fixed
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
haproxy
bionic
not-affected
focal
not-affected
jammy
not-affected
noble
Fixed 2.8.16-0ubuntu0.24.04.2
released
questing
Fixed 3.0.12-0ubuntu0.25.10.4
released
resolute
Fixed 3.2.9-1ubuntu2.1
released
xenial
not-affected
Azure Linux logo
Azure Linux Releases
Azure Package
Release
haproxy
Azure Linux 3.0
0:2.9.11-5.azl3
fixed
Common Weakness Enumeration
References
https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84
https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html
https://www.haproxy.com/documentation/haproxy-aloha/changelog/
https://www.haproxy.org
https://www.mail-archive.com/haproxy@formilux.org/msg46752.html
https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html