TI-2026-25946 Aliases CVE-2026-33555 GHSA-5mp8-rq5m-pj7m

An issue was discovered in HAProxy before 3.3.6.

MEDIUM 59CWE-130Published 2026-04-13 · Updated 2026-10-18

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: None · Low · None
Fix status: Partial Red Hat: 1 fixed, 3 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00307 23rd percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Partial HAProxy (HAProxy): 3.3.6Red Hat: 1 advisoryRed Hat: 1 fixed, 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
HAProxy	HAProxy	2.6 to before 3.3.6	3.3.6	Patch available	CNA

HAProxy VendorHAProxy Affected 2.6 to before 3.3.6 Fixed in 3.3.6 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:haproxy:haproxy::::::::	2.6.0 to before 3.3.6	Vulnerable	HAProxy

cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:* Versions 2.6.0 to before 3.3.6 Vulnerable ·HAProxy

Remediation

Fix · CNA HAProxy (HAProxy) Fixed in 3.3.6

Red Hat 1 advisory

RHSA-2026:8749 Released 2026-04-17 · Red Hat rating Moderate
Red Hat Hardened Images RPMs bug fix and enhancement update
- Red Hat Hardened Images haproxy-3.0.19-1.1.hum1@aarch64, haproxy-3.0.19-1.1.hum1@src, haproxy-3.0.19-1.1.hum1@x86_64

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat Enterprise Linux 10	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 9	Affected	No fix yet: Fix deferred
Red Hat OpenShift Container Platform 4	Affected	No fix yet: Fix deferred
Red Hat Hardened Images	Fixed	RHSA-2026:8749

Not affected: 2 products

Red Hat Enterprise Linux 7
Red Hat Enterprise Linux 8

Timeline

2026-10-02 Threatist record created from CVE-2026-33555
2026-10-03 Alias added: GHSA-5mp8-rq5m-pj7m

References

Exploit 1

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

Patch 1

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

Other 3

TI-2020-08973 In hpack_dht_insert in hpack-tbl.c in the HPACK decoder in HAProxy 1.8 through 2.x before… CVSS 3.1HIGH 8.8
TI-2023-21094 HAProxy through 2.0.32, 2.1.x and 2.2.x through 2.2.30, 2.3.x and 2.4.x through 2.4.23… CVSS 3.1HIGH 7.2
TI-2019-10602 HAProxy through 2.0.2 allows attackers to cause a denial of service (ha_panic) via… CVSS 3.0HIGH 7.5
TI-2021-17418 An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be… CVSS 3.1HIGH 7.5
TI-2016-04651 HAproxy 1.6.x before 1.6.6, when a deny comes from a reqdeny rule, allows remote… CVSS 3.0HIGH 7.5
TI-2023-10998 HAProxy before 2.7.3 may allow a bypass of access control because HTTP/1 headers are… CVSS 3.1CRITICAL 9.1

See all 35 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences