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
mitreCNA
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: Unknown
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
haproxyhaproxy
2.6 ≤
𝑥
< 3.3.6
CNA
Debian logo
Debian Releases
Debian Product
Codename
haproxy
bookworm
vulnerable
bookworm (security)
vulnerable
bullseye
vulnerable
bullseye (security)
vulnerable
forky
3.2.15-1
fixed
sid
3.2.15-1
fixed
trixie
vulnerable
trixie (security)
vulnerable
Common Weakness Enumeration
References
https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84
https://www.haproxy.com/documentation/haproxy-aloha/changelog/
https://www.haproxy.org
https://www.mail-archive.com/haproxy@formilux.org/msg46752.html