---
title: "CVE-2026-90678: HAProxy - HTTP Request Smuggling"
description: "HAProxy 3.3.0 through 3.4.4 and 3.5-dev1 through 3.5-dev5 contain an HTTP request smuggling vulnerability caused by improper handling of HTTP/3 DATA frame lengths in chunked transfer coding on reused HTTP/1.1 backend connections, letting remote unauthenticated clients smuggle requests past frontend rules, exploit requires HTTP/3 frontend with QUIC support and specific backend conditions."
url: https://panop.io/threat-heartbeat/CVE-2026-90678/
---

# CVE-2026-90678 HAProxy - HTTP Request Smuggling

HAProxy 3.3.0 through 3.4.4 and 3.5-dev1 through 3.5-dev5 contain an HTTP request smuggling vulnerability caused by improper handling of HTTP/3 DATA frame lengths in chunked transfer coding on reused HTTP/1.1 backend connections, letting remote unauthenticated clients smuggle requests past frontend rules, exploit requires HTTP/3 frontend with QUIC support and specific backend conditions.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.77% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-90678)

## Details

Type

HTTP Request Smuggling

Impact

Broken Access Control

CVSS vector

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

Published

13 September 2026

Updated

15 October 2026

Weakness

[CWE-130](https://cwe.mitre.org/data/definitions/130.html)

## Vendor fix

Upgrade to a version later than 3.4.4 or 3.5-dev5 or the latest available version.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-90678](https://nvd.nist.gov/vuln/detail/CVE-2026-90678)
- [http://git.haproxy.org/?p=haproxy.git;a=commit;h=86a4ebc761a278838e8cb06f3a292282ba704c65](http://git.haproxy.org/?p=haproxy.git;a=commit;h=86a4ebc761a278838e8cb06f3a292282ba704c65)
- [https://github.com/haproxy/haproxy/commit/86a4ebc761a278838e8cb06f3a292282ba704c65](https://github.com/haproxy/haproxy/commit/86a4ebc761a278838e8cb06f3a292282ba704c65)
- [https://www.haproxy.org/download/3.5/src/CHANGELOG](https://www.haproxy.org/download/3.5/src/CHANGELOG)

[← All CVEs](https://panop.io/threat-heartbeat/)

## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

[Book a demo](https://panop.io/demo)