CVE-2026-28369 is a high-severity (CVSS 8.7) CWE-444 vulnerability in io.undertow:undertow-core. A fix is available for io.undertow:undertow-core — see the affected versions and patch details below.
Undertow is Vulnerable to HTTP Request/Response Smuggling
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28369.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
io.undertow:undertow-core☕io.undertow:undertow-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.undertow:undertow-core | all versions | 2.2.40.Finalio.undertow:undertow-core:2.2.40.Final |
| ☕Maven | io.undertow:undertow-core | ≥ 2.3.0.Final&&< 2.3.25.Final | 2.3.25.Finalio.undertow:undertow-core:2.3.25.Final |
Affected Products
build of apache camel - hawtioredhatbuild of apache camel for spring bootredhatdata gridredhatenterprise linuxredhatfuseredhatjboss enterprise application platformredhatDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.undertow:undertow-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.undertow:undertow-core to 2.2.40.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28369 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat JBoss Enterprise Application Platform 8.1.6 | io.undertow/undertow-core:2.3.24.SP2-redhat-00001 | RHSA-2026:25126 |
| Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 | eap8-activemq-artemis-0:2.40.0-7.redhat_00015.1.el8eap | RHSA-2026:25125 |
Frequently Asked Questions
Is CVE-2026-28369 in your dependencies?
Find it across Maven, including transitive dependencies.