CVE-2020-11996
HIGHCVE-2020-11996 is a high-severity (CVSS 7.5) vulnerability in org.apache.tomcat:tomcat. 2 public exploit references exist, so weaponization risk is real. O3 Security confirms whether CVE-2020-11996 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Uncontrolled Resource Consumption in Apache Tomcat
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-2020-11996 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 0 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
org.apache.tomcat:tomcat☕org.apache.tomcat:tomcat☕org.apache.tomcat:tomcat☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-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 specially crafted sequence of HTTP/2 requests sent to Apache Tomcat 10.0.0-M1 to 10.0.0-M5, 9.0.0.M1 to 9.0.35 and 8.5.0 to 8.5.55 could trigger high CPU usage for several seconds. If a sufficient number of such requests were made on concurrent HTTP/2 connections, the server could become unresponsive.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.tomcat:tomcat | ≥ 10.0.0-M1&&< 10.0.0-M5 | 10.0.0-M5 |
| ☕Maven | org.apache.tomcat:tomcat | ≥ 9.0.0.M1&&< 9.0.35 | 9.0.35 |
| ☕Maven | org.apache.tomcat:tomcat | ≥ 8.5.0&&< 8.5.55 | 8.5.55 |
| ☕Maven | org.apache.tomcat.embed:tomcat-embed-core | ≥ 10.0.0-M1&&< 10.0.0-M5 | 10.0.0-M5 |
| ☕Maven | org.apache.tomcat.embed:tomcat-embed-core | ≥ 9.0.0.M1&&< 9.0.35 | 9.0.35 |
| ☕Maven | org.apache.tomcat.embed:tomcat-embed-core | ≥ 8.5.0&&< 8.5.55 | 8.5.55 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.tomcat:tomcat. 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 org.apache.tomcat:tomcat to 10.0.0-M5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-11996 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-2020-11996 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-2020-11996. 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.
Red Hat OpenStack Platform's OpenDaylight will not be updated for this flaw because it was deprecated as of RHOSP14 and is only receiving security fixes for Important and Critical flaws. Apache Tomcat versions as shipped with Red Hat Enterprise Linux 6 and 7 are not affected by this flaw as it doesn't support HTTP/2…
Frequently Asked Questions
Is CVE-2020-11996 in your dependencies?
O3 detects CVE-2020-11996 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.