# CVE-2026-28367: Undertow: undertow: request smuggling via `\r\r\r` as a header block terminator

> Remote attackers can perform request smuggling via malformed header terminators, leading to unauthorized access or request manipulation in Undertow.

- **Severity:** High 8.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Mar 2026
- **Updated:** 14 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-28367, GHSA-3gv6-g396-9v4r, UBUNTU-CVE-2026-28367

## What is CVE-2026-28367?

CVE-2026-28367 is a high-severity vulnerability in Redhat Jboss Enterprise Application Platform, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in Undertow. A remote attacker can exploit this vulnerability by sending `\r\r\r` as a header block terminator. This can be used for request smuggling with certain proxy servers, such as older versions of Apache Traffic Server and Google Cloud Classic Application Load Balancer, potentially leading to unauthorized access or manipulation of web requests.

Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2026-28367?

2 open source packages ship an affected version, including io.undertow:undertow-parent. It affects 9 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.undertow:undertow-parent` | Maven | All versions to 2.3.23.Final | None |
| `io.undertow:undertow-parent` | Maven | All versions to 2.3.23.Final | None |

Products: Redhat Build of Apache Camel - Hawtio, Redhat Build of Apache Camel for Spring Boot, Redhat Data Grid, Redhat Fuse, Redhat Jboss Enterprise Application Platform, Redhat Jboss Enterprise Application Platform Expansion Pack, Redhat Process Automation, Redhat Single Sign-On, Redhat Undertow.

## How do I fix CVE-2026-28367?

Upgrade to a fixed version.

## Is CVE-2026-28367 being exploited?

There is no known exploitation of CVE-2026-28367 in the wild and no public exploit code.

## Other vulnerabilities in Redhat Jboss Enterprise Application Platform

- [CVE-2026-28368](https://insights.sbomify.com/CVE-2026-28368/): Undertow: undertow: request smuggling via inconsistent header parsing (high 8.7)
- [CVE-2026-28369](https://insights.sbomify.com/CVE-2026-28369/): Undertow: undertow: request smuggling via malformed http request headers (high 8.7)
- [CVE-2024-7885](https://insights.sbomify.com/CVE-2024-7885/): Undertow: improper state management in proxy protocol parsing causes information leakage (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28367 and fix it if it is affected.

What it is: CVE-2026-28367 is a high-severity vulnerability in Redhat Jboss Enterprise Application Platform, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-28367 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.undertow:undertow-parent (Maven): affected all versions up to 2.3.23.Final; no fix listed
- io.undertow:undertow-parent (Maven): affected all versions up to 2.3.23.Final; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-28367/ (Markdown: https://insights.sbomify.com/CVE-2026-28367/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28367
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28367
- OSV: https://osv.dev/vulnerability/CVE-2026-28367

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28367/
Summaries are generated and may contain mistakes; the official description above is the record.