# CVE-2020-11996: Uncontrolled Resource Consumption in Apache Tomcat > Attackers can cause Apache Tomcat to become unresponsive by sending crafted HTTP/2 requests that trigger high CPU usage. - **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 Jun 2020 - **Updated:** 8 Oct 2026 - **Also known as:** BIT-tomcat-2020-11996, DEBIAN-CVE-2020-11996, GHSA-53hp-jpwq-2jgq, RHSA-2020:5170, SUSE-SU-2020:1841-1, SUSE-SU-2020:1962-1, SUSE-SU-2020:1963-1, SUSE-SU-2020:1983-1, UBUNTU-CVE-2020-11996, openSUSE-SU-2020:1051-1, openSUSE-SU-2020:1063-1 ## What is CVE-2020-11996? CVE-2020-11996 is a high-severity denial of service vulnerability in Apache Tomcat, published on 26 Jun 2020. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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. ## Which versions are affected by CVE-2020-11996? 13 open source packages ship an affected version, including org.apache.tomcat.embed:tomcat-embed-core, tomcat and org.apache.tomcat:tomcat. It affects 8 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.apache.tomcat.embed:tomcat-embed-core` | Maven | From 10.0.0-M1 | 10.0.0-M5 | | `org.apache.tomcat.embed:tomcat-embed-core` | Maven | From 10.0.0-M1 | 10.0.0-M5 | | `org.apache.tomcat.embed:tomcat-embed-core` | Maven | From 8.5.0 | 8.5.55 | | `org.apache.tomcat.embed:tomcat-embed-core` | Maven | From 8.5.0 | 8.5.55 | | `org.apache.tomcat.embed:tomcat-embed-core` | Maven | From 9.0.0.M1 | 9.0.35 | | `org.apache.tomcat.embed:tomcat-embed-core` | Maven | From 9.0.0.M1 | 9.0.35 | | `tomcat` | Bitnami | From 8.5.0 | 8.5.56, 9.0.36 | | `org.apache.tomcat:tomcat` | Maven | From 10.0.0-M1 | 10.0.0-M5 | | `org.apache.tomcat:tomcat` | Maven | From 10.0.0-M1 | 10.0.0-M5 | | `org.apache.tomcat:tomcat` | Maven | From 8.5.0 | 8.5.55 | | `org.apache.tomcat:tomcat` | Maven | From 8.5.0 | 8.5.55 | | `org.apache.tomcat:tomcat` | Maven | From 9.0.0.M1 | 9.0.35 | | `org.apache.tomcat:tomcat` | Maven | From 9.0.0.M1 | 9.0.35 | | `jws5-jboss-logging` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:3.4.1-1.Final_redhat_00001.1.el6jws | | `jws5-mod_cluster` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:1.4.2-7.Final_redhat_00002.2.el6jws | | `jws5-mod_cluster-tomcat` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:1.4.2-7.Final_redhat_00002.2.el6jws | | `jws5-tomcat` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-admin-webapps` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-docs-webapp` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-el-3.0-api` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-javadoc` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-jsp-2.3-api` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-lib` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-native` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:1.2.25-2.redhat_2.el6jws | | `jws5-tomcat-native-debuginfo` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:1.2.25-2.redhat_2.el6jws | | `jws5-tomcat-selinux` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-servlet-4.0-api` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-tomcat-webapps` | Red Hat:jboss_enterprise_web_server:5.4::el6 | All versions | 0:9.0.36-6.redhat_5.2.el6jws | | `jws5-jboss-logging` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:3.4.1-1.Final_redhat_00001.1.el7jws | | `jws5-mod_cluster` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:1.4.2-7.Final_redhat_00002.2.el7jws | | `jws5-mod_cluster-tomcat` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:1.4.2-7.Final_redhat_00002.2.el7jws | | `jws5-tomcat` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-admin-webapps` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-docs-webapp` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-el-3.0-api` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-javadoc` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-jsp-2.3-api` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-lib` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:9.0.36-6.redhat_5.2.el7jws | | `jws5-tomcat-native` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:1.2.25-2.redhat_2.el7jws | | `jws5-tomcat-native-debuginfo` | Red Hat:jboss_enterprise_web_server:5.4::el7 | All versions | 0:1.2.25-2.redhat_2.el7jws | Products: Apache Tomcat, Canonical Ubuntu Linux, Debian Debian Linux, Netapp Oncommand System Manager, Opensuse Leap, Oracle Mysql Enterprise Monitor, Oracle Siebel Ui Framework, Oracle Workload Manager. ## How do I fix CVE-2020-11996? Upgrade org.apache.tomcat.embed:tomcat-embed-core to a fixed version for your release line: 10.0.0-M5, 8.5.55 or 9.0.35. ## Is CVE-2020-11996 being exploited? There is no known exploitation of CVE-2020-11996 in the wild and no public exploit code. Public exploit code: - tomcat-embed-core-9.0.31 CVE-2020-11996 Test PoC (github_poc): https://github.com/rusakovichma/tomcat-embed-core-9.0.31-CVE-2020-11996 ## Other vulnerabilities in Apache Tomcat - [CVE-2025-24813](https://insights.sbomify.com/CVE-2025-24813/): Apache Tomcat Path Equivalence (critical 10.0, exploited in the wild) - [CVE-2016-8735](https://insights.sbomify.com/CVE-2016-8735/): Apache Tomcat Remote Code Execution (critical 9.8, exploited in the wild) - [CVE-2017-12617](https://insights.sbomify.com/CVE-2017-12617/): Apache Tomcat Remote Code Execution (high 8.1, exploited in the wild) - [CVE-2017-12615](https://insights.sbomify.com/CVE-2017-12615/): Apache Tomcat on Windows Remote Code Execution (high 8.1, exploited in the wild) - [CVE-2026-34486](https://insights.sbomify.com/CVE-2026-34486/): Apache Tomcat Missing Encryption of Sensitive Data (high 7.5, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2020-11996 and fix it if it is affected. What it is: CVE-2020-11996 is a high-severity denial of service vulnerability in Apache Tomcat, published on 26 Jun 2020. 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-2020-11996 in the wild and no public exploit code. Affected packages and fixed versions: - org.apache.tomcat.embed:tomcat-embed-core (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M5 - org.apache.tomcat.embed:tomcat-embed-core (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M5 - org.apache.tomcat.embed:tomcat-embed-core (Maven): affected from 8.5.0; fixed in 8.5.55 - org.apache.tomcat.embed:tomcat-embed-core (Maven): affected from 8.5.0; fixed in 8.5.55 - org.apache.tomcat.embed:tomcat-embed-core (Maven): affected from 9.0.0.M1; fixed in 9.0.35 - org.apache.tomcat.embed:tomcat-embed-core (Maven): affected from 9.0.0.M1; fixed in 9.0.35 - tomcat (Bitnami): affected from 8.5.0; fixed in 8.5.56, 9.0.36 - org.apache.tomcat:tomcat (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M5 - org.apache.tomcat:tomcat (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M5 - org.apache.tomcat:tomcat (Maven): affected from 8.5.0; fixed in 8.5.55 - org.apache.tomcat:tomcat (Maven): affected from 8.5.0; fixed in 8.5.55 - org.apache.tomcat:tomcat (Maven): affected from 9.0.0.M1; fixed in 9.0.35 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-2020-11996/ (Markdown: https://insights.sbomify.com/CVE-2020-11996/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2020-11996 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-11996 - OSV: https://osv.dev/vulnerability/CVE-2020-11996 --- From sbomify Insights: https://insights.sbomify.com/CVE-2020-11996/ Summaries are generated and may contain mistakes; the official description above is the record.