CVE-2021-3629 — undertow-core
MEDIUMCVE-2021-3629 is a medium-severity (CVSS 5.9) Uncontrolled Resource Consumption vulnerability in io.undertow:undertow-core. A fix is available for io.undertow:undertow-core — see the affected versions and patch details below.
Undertow Uncontrolled Resource Consumption
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-3629 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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. A potential security issue in flow control handling by the browser over http/2 may potentially cause overhead or a denial of service in the server. The highest threat from this vulnerability is availability. This flaw affects Undertow versions prior to 2.0.40.Final and prior to 2.2.11.Final.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.undertow:undertow-core | all versions | 2.0.40.Finalio.undertow:undertow-core:2.0.40.Final |
| ☕Maven | io.undertow:undertow-core | ≥ 2.1.0&&< 2.2.11.Final | 2.2.11.Finalio.undertow:undertow-core:2.2.11.Final |
Detection & 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 2.0.40.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3629 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-3629 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-3629. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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 |
|---|---|---|
| EAP 7.3.10 GA | undertow | RHSA-2021:5154 |
| Red Hat EAP-XP 2 via EAP 7.3.x base | undertow | RHSA-2022:0146 |
| Red Hat Fuse 7.10 | undertow | RHSA-2021:5134 |
| Red Hat Fuse 7.11 | see advisory | RHSA-2022:5532 |
| Red Hat Integration Camel Quarkus 2 | see advisory | RHSA-2021:4767 |
| Red Hat JBoss Enterprise Application Platform | io.undertow/undertow-core:2.2.12.Final-redhat-00001 | RHSA-2021:4679 |
| Red Hat JBoss Enterprise Application Platform 7.3 for RHEL 6 | eap7-apache-cxf-0:3.3.12-1.redhat_00001.1.el6eap | RHSA-2021:5149 |
| Red Hat JBoss Enterprise Application Platform 7.3 for RHEL 7 | eap7-apache-cxf-0:3.3.12-1.redhat_00001.1.el7eap | RHSA-2021:5150 |
Frequently Asked Questions
Is CVE-2021-3629 in your dependencies?
O3 Security finds CVE-2021-3629 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.