# CVE-2021-3859: Undertow vulnerable to Denial of Service (DoS) attacks

> An attacker can cause a denial of service in Undertow by triggering client-side invocation timeouts over HTTP2.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Aug 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3859, GHSA-339q-62wm-c39w, RHSA-2022:0405, UBUNTU-CVE-2021-3859

## What is CVE-2021-3859?

CVE-2021-3859 is a high-severity denial of service vulnerability in Netapp Cloud Secure Agent, published on 26 Aug 2022. 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 that tripped the client-side invocation timeout with certain calls made over HTTP2. This flaw allows an attacker to carry out denial of service attacks.

Weakness: CWE-668 (Exposure of Resource to Wrong Sphere), CWE-214 (Invocation of Process Using Visible Sensitive Information)

## Which versions are affected by CVE-2021-3859?

2 open source packages ship an affected version, including io.undertow:undertow-core. It affects 6 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.undertow:undertow-core` | Maven | All versions | 2.2.15 |
| `io.undertow:undertow-core` | Maven | All versions | 2.2.15 |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.3::el6 | All versions | 0:2.0.41-2.SP2_redhat_00001.1.el6eap |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.3::el7 | All versions | 0:2.0.41-2.SP2_redhat_00001.1.el7eap |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.3::el8 | All versions | 0:2.0.41-2.SP2_redhat_00001.1.el8eap |

Products: Netapp Cloud Secure Agent, Netapp Oncommand Insight, Netapp Oncommand Workflow Automation, Redhat Jboss Enterprise Application Platform, Redhat Single Sign-On, Redhat Undertow.

## How do I fix CVE-2021-3859?

Upgrade io.undertow:undertow-core to 2.2.15 or later.

## Is CVE-2021-3859 being exploited?

There is no known exploitation of CVE-2021-3859 in the wild and no public exploit code.

## Other vulnerabilities in Netapp Cloud Secure Agent

- [CVE-2022-22971](https://insights.sbomify.com/CVE-2022-22971/): Allocation of Resources Without Limits or Throttling in Spring Framework (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3859 and fix it if it is affected.

What it is: CVE-2021-3859 is a high-severity denial of service vulnerability in Netapp Cloud Secure Agent, published on 26 Aug 2022. 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-2021-3859 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.2.15
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.2.15

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-2021-3859/ (Markdown: https://insights.sbomify.com/CVE-2021-3859/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3859
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3859
- OSV: https://osv.dev/vulnerability/CVE-2021-3859

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3859/
Summaries are generated and may contain mistakes; the official description above is the record.