---
id: "CVE-2026-28369"
kind: "vulnerability"
aliases: ["CVE-2026-28369", "GHSA-vqqj-9cmv-hx43"]
title: "Undertow is Vulnerable to HTTP Request/Response Smuggling"
severity: "critical"
cvss: 9.1
epss: 0.00689
exploited: false
status: "open"
category: "package"
products: [{"name": "io.undertow:undertow-core", "fixed": ["2.2.40.Final"], "affected": "< 2.2.40.Final", "ecosystem": "maven"}, {"name": "io.undertow:undertow-core", "fixed": ["2.3.25.Final"], "affected": ">= 2.3.0.Final, < 2.3.25.Final", "ecosystem": "maven"}, {"name": "redhat build of apache camel - hawtio", "fixed": [], "affected": "= 4.0", "ecosystem": "vendor"}, {"name": "redhat build of apache camel for spring boot", "fixed": [], "affected": "= 4.0", "ecosystem": "vendor"}, {"name": "redhat data grid", "fixed": [], "affected": "= 8.0", "ecosystem": "vendor"}, {"name": "redhat fuse", "fixed": [], "affected": "= 7.0.0", "ecosystem": "vendor"}, {"name": "redhat jboss enterprise application platform", "fixed": [], "affected": "= 7.0.0", "ecosystem": "vendor"}, {"name": "redhat jboss enterprise application platform", "fixed": [], "affected": "= 8.0.0", "ecosystem": "vendor"}, {"name": "redhat jboss enterprise application platform expansion pack", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "redhat process automation", "fixed": [], "affected": "= 7.0", "ecosystem": "vendor"}, {"name": "redhat single sign-on", "fixed": [], "affected": "= 7.0", "ecosystem": "vendor"}, {"name": "redhat undertow", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "redhat enterprise linux", "fixed": [], "affected": "= 9.0", "ecosystem": "vendor"}]
ecosystems: ["maven", "vendor"]
tags: ["cwe-444", "java", "maven", "package", "reverse-proxy", "undertow"]
not_affected_if: ["no-undertow-core-dependency", "version-below-affected-range"]
published_at: "2026-03-27T17:16:28+00:00"
first_seen_at: "2026-11-04T20:45:52+00:00"
updated_at: "2026-11-04T20:59:06+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-vqqj-9cmv-hx43", "first_seen_at": "2026-11-04T20:45:52+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-28369", "first_seen_at": "2026-11-04T20:59:06+00:00"}]
exploit_sources: [{"type": "epss", "score": 0.00689, "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-28369"}]
---

# Undertow is Vulnerable to HTTP Request/Response Smuggling

Undertow, a Java web server library, strips leading spaces from the first HTTP header line when it should reject them. A remote attacker can use this to smuggle requests past proxies and reach restricted paths or poison caches.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- maven:io.undertow:undertow-core affected < 2.2.40.Final fixed 2.2.40.Final
- maven:io.undertow:undertow-core affected >= 2.3.0.Final, < 2.3.25.Final fixed 2.3.25.Final
- vendor:redhat build of apache camel - hawtio affected = 4.0 fixed ?
- vendor:redhat build of apache camel for spring boot affected = 4.0 fixed ?
- vendor:redhat data grid affected = 8.0 fixed ?
- vendor:redhat fuse affected = 7.0.0 fixed ?
- vendor:redhat jboss enterprise application platform affected = 7.0.0 fixed ?
- vendor:redhat jboss enterprise application platform affected = 8.0.0 fixed ?
- vendor:redhat jboss enterprise application platform expansion pack affected ? fixed ?
- vendor:redhat process automation affected = 7.0 fixed ?
- vendor:redhat single sign-on affected = 7.0 fixed ?
- vendor:redhat undertow affected ? fixed ?
- vendor:redhat enterprise linux affected = 9.0 fixed ?

## How to check

- Run `mvn dependency:tree` and look for `io.undertow:undertow-core` and its version
- Check whether any version is below `2.2.40.Final` or in the range `2.3.0.Final` to `2.3.25.Final`

## Fix

- Upgrade to `2.2.40.Final` on the 2.2 line
- Upgrade to `2.3.25.Final` on the 2.3 line

## Timeline

- 2026-11-04T20:45:52+00:00 ghsa https://github.com/advisories/GHSA-vqqj-9cmv-hx43
- 2026-11-04T20:59:06+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-28369

## Documents

- [advisory] Vendor advisory: access.redhat.com https://access.redhat.com/security/cve/CVE-2026-28369
- [advisory] Vendor advisory: bugzilla.redhat.com https://bugzilla.redhat.com/show_bug.cgi?id=2443262
- [fix] Patch: github.com https://github.com/undertow-io/undertow/commit/3ece0bf2b2cf5e01db8ca25e41b831e66d3f5961
- [fix] Patch: github.com https://github.com/undertow-io/undertow/commit/904e26f1be62fb00b440538608a9574839821878
- [fix] Patch: github.com https://github.com/undertow-io/undertow/commit/c5dc41479e9c3576552d7e98e31bb1c237ae155e

## From the sources

A flaw was found in Undertow. When Undertow receives an HTTP request where the first header line starts with one or more spaces, it incorrectly processes the request by stripping these leading spaces. This behavior, which violates HTTP standards, can be exploited by a remote attacker to perform request smuggling. Request smuggling allows an attacker to bypass security mechanisms, access restricted information, or manipulate web caches, potentially leading to unauthorized actions or data exposure.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_