CVE-2021-3597
MEDIUMCVE-2021-3597 is a medium-severity (CVSS 5.9) CWE-362 vulnerability in io.undertow:undertow-core. O3 Security confirms whether CVE-2021-3597 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
undertow Race Condition vulnerability
Blast Radius
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. The HTTP2SourceChannel fails to write the final frame under some circumstances, resulting in a denial of service. The highest threat from this vulnerability is availability. This flaw affects Undertow versions prior to 2.0.35.SP1, prior to 2.2.6.SP1, prior to 2.2.7.SP1, prior to 2.0.36.SP1, prior to 2.2.9.Final and prior to 2.0.39.Final.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.undertow:undertow-core | ≥ 2.1.0&&< 2.2.9.Final | 2.2.9.Final |
| ☕Maven | io.undertow:undertow-core | all versions | 2.0.39.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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update io.undertow:undertow-core to 2.2.9.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3597 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 pinpoints whether CVE-2021-3597 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-3597. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-3597 in your dependencies?
O3 detects CVE-2021-3597 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.