# CVE-2021-3690: Undertow vulnerable to memory exhaustion due to buffer leak

> An attacker can cause a denial of service in Undertow by triggering a buffer leak via WebSocket PONG messages, leading to memory exhaustion.

- **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:** 23 Aug 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3690, GHSA-fj7c-vg2v-ccrm, RHSA-2021:3217, RHSA-2021:3219, UBUNTU-CVE-2021-3690

## What is CVE-2021-3690?

CVE-2021-3690 is a high-severity denial of service vulnerability in Redhat Jboss Enterprise Application Platform, published on 23 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. A buffer leak on the incoming WebSocket PONG message may lead to memory exhaustion. This flaw allows an attacker to cause a denial of service. The highest threat from this vulnerability is availability.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-3690?

4 open source packages ship an affected version, including io.undertow:undertow-core. It affects 7 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.undertow:undertow-core` | Maven | All versions | 2.0.40 |
| `io.undertow:undertow-core` | Maven | All versions | 2.0.40 |
| `io.undertow:undertow-core` | Maven | From 2.2.0 | 2.2.10 |
| `io.undertow:undertow-core` | Maven | From 2.2.0 | 2.2.10 |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.3::el6 | All versions | 0:2.0.38-2.SP2_redhat_00001.1.el6eap |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.3::el7 | All versions | 0:2.0.38-2.SP2_redhat_00001.1.el7eap |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.3::el8 | All versions | 0:2.0.38-2.SP2_redhat_00001.1.el8eap |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.4::el7 | All versions | 0:2.2.5-2.SP1_redhat_00001.1.el7eap |
| `eap7-undertow` | Red Hat:jboss_enterprise_application_platform:7.4::el8 | All versions | 0:2.2.5-2.SP1_redhat_00001.1.el8eap |

Products: Redhat Fuse, Redhat Integration Camel K, Redhat Integration Camel Quarkus, Redhat Jboss Enterprise Application Platform, Redhat Openshift Application Runtimes, Redhat Single Sign-On, Redhat Undertow.

## How do I fix CVE-2021-3690?

Upgrade io.undertow:undertow-core to a fixed version for your release line: 2.0.40 or 2.2.10.

## Is CVE-2021-3690 being exploited?

There is no known exploitation of CVE-2021-3690 in the wild and no public exploit code.

## Other vulnerabilities in Redhat Jboss Enterprise Application Platform

- [CVE-2026-41731](https://insights.sbomify.com/CVE-2026-41731/): In Spring for Apache Kafka, overly broad trusted-package matching in header mappers exposes JDK classes to deserialization (high 8.1)
- [CVE-2019-14860](https://insights.sbomify.com/CVE-2019-14860/): Misconfiguration in syndesis (high 7.4)
- [CVE-2025-57849](https://insights.sbomify.com/CVE-2025-57849/): Fuse: privilege escalation via excessive /etc/passwd permissions (medium 6.4)
- [CVE-2020-10688](https://insights.sbomify.com/CVE-2020-10688/): Cross-site scripting in RESTEasy (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3690 and fix it if it is affected.

What it is: CVE-2021-3690 is a high-severity denial of service vulnerability in Redhat Jboss Enterprise Application Platform, published on 23 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-2021-3690 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.0.40
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.0.40
- io.undertow:undertow-core (Maven): affected from 2.2.0; fixed in 2.2.10
- io.undertow:undertow-core (Maven): affected from 2.2.0; fixed in 2.2.10

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-2021-3690/ (Markdown: https://insights.sbomify.com/CVE-2021-3690/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3690
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3690
- OSV: https://osv.dev/vulnerability/CVE-2021-3690

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3690/
Summaries are generated and may contain mistakes; the official description above is the record.