# CVE-2020-13935: Infinite Loop in Apache Tomcat > Attackers can cause a denial of service in Apache Tomcat by sending WebSocket frames with invalid payload lengths, triggering an infinite loop. - **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:** 14 Jul 2020 - **Updated:** 8 Oct 2026 - **Also known as:** BIT-tomcat-2020-13935, CLSA-2026-1777446601, DEBIAN-CVE-2020-13935, GHSA-m7jv-hq7h-mq7c, RHSA-2020:3383, UBUNTU-CVE-2020-13935 ## What is CVE-2020-13935? CVE-2020-13935 is a high-severity denial of service vulnerability in Apache Tomcat, published on 14 Jul 2020. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description The payload length in a WebSocket frame was not correctly validated in Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M1 to 9.0.36, 8.5.0 to 8.5.56 and 7.0.27 to 7.0.104. Invalid payload lengths could trigger an infinite loop. Multiple requests with invalid payload lengths could lead to a denial of service. Weakness: CWE-835 (Loop with Unreachable Exit Condition) ## Which versions are affected by CVE-2020-13935? 25 open source packages ship an affected version, including org.apache.tomcat.embed:tomcat-embed-websocket, tomcat and org.apache.tomcat:tomcat. It affects 18 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 10.0.0-M1 | 10.0.0-M7 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 10.0.0-M1 | 10.0.0-M7 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 7.0.27 | 7.0.105 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 7.0.27 | 7.0.105 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 8.5.0 | 8.5.57 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 8.5.0 | 8.5.57 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 9.0.0.M1 | 9.0.37 | | `org.apache.tomcat.embed:tomcat-embed-websocket` | Maven | From 9.0.0.M1 | 9.0.37 | | `tomcat` | Bitnami | From 7.0.27 | 7.0.105, 8.5.57, 9.0.37 | | `org.apache.tomcat:tomcat` | Maven | From 10.0.0-M1 | 10.0.0-M7 | | `org.apache.tomcat:tomcat` | Maven | From 10.0.0-M1 | 10.0.0-M7 | | `org.apache.tomcat:tomcat` | Maven | From 7.0.27 | 7.0.105 | | `org.apache.tomcat:tomcat` | Maven | From 7.0.27 | 7.0.105 | | `org.apache.tomcat:tomcat` | Maven | From 8.5.0 | 8.5.57 | | `org.apache.tomcat:tomcat` | Maven | From 8.5.0 | 8.5.57 | | `org.apache.tomcat:tomcat` | Maven | From 9.0.0.M1 | 9.0.37 | | `org.apache.tomcat:tomcat` | Maven | From 9.0.0.M1 | 9.0.37 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 10.0.0-M1 | 10.0.0-M7 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 10.0.0-M1 | 10.0.0-M7 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 7.0.27 | 7.0.105 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 7.0.27 | 7.0.105 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 8.5.0 | 8.5.57 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 8.5.0 | 8.5.57 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 9.0.0.M1 | 9.0.37 | | `org.apache.tomcat:tomcat-websocket` | Maven | From 9.0.0.M1 | 9.0.37 | | `jbossweb` | Red Hat:jboss_enterprise_application_platform:6::el5 | All versions | 0:7.5.31-2.Final_redhat_2.1.ep6.el5 | | `jbossweb` | Red Hat:jboss_enterprise_application_platform:6::el6 | All versions | 0:7.5.31-2.Final_redhat_2.1.ep6.el6 | | `jbossweb` | Red Hat:jboss_enterprise_application_platform:6::el7 | All versions | 0:7.5.31-2.Final_redhat_2.1.ep6.el7 | Products: Apache Tomcat, Canonical Ubuntu Linux, Debian Debian Linux, Mcafee Epolicy Orchestrator, Netapp Oncommand System Manager, Opensuse Leap, Oracle Agile Engineering Data Management, Oracle Agile Product Lifecycle Management, Oracle Blockchain Platform, Oracle Commerce Guided Search, Oracle Communications Cloud Native Core Policy, Oracle Communications Instant Messaging Server, Oracle Fmw Platform, Oracle Instantis Enterprisetrack, Oracle Managed File Transfer, Oracle Mysql Enterprise Monitor, Oracle Siebel Ui Framework, Oracle Workload Manager. ## How do I fix CVE-2020-13935? Upgrade org.apache.tomcat.embed:tomcat-embed-websocket to a fixed version for your release line: 10.0.0-M7, 7.0.105, 8.5.57 or 9.0.37. ## Is CVE-2020-13935 being exploited? There is no known exploitation of CVE-2020-13935 in the wild and no public exploit code. Public exploit code: - Exploit for WebSocket Vulnerability in Apache Tomcat (github_poc): https://github.com/RedTeamPentesting/CVE-2020-13935 - https://github.com/aabbcc19191/CVE-2020-13935 (github_poc): https://github.com/aabbcc19191/CVE-2020-13935 ## 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-2020-13935 and fix it if it is affected. What it is: CVE-2020-13935 is a high-severity denial of service vulnerability in Apache Tomcat, published on 14 Jul 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-2020-13935 in the wild and no public exploit code. Affected packages and fixed versions: - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M7 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M7 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 7.0.27; fixed in 7.0.105 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 7.0.27; fixed in 7.0.105 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 8.5.0; fixed in 8.5.57 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 8.5.0; fixed in 8.5.57 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 9.0.0.M1; fixed in 9.0.37 - org.apache.tomcat.embed:tomcat-embed-websocket (Maven): affected from 9.0.0.M1; fixed in 9.0.37 - tomcat (Bitnami): affected from 7.0.27; fixed in 7.0.105, 8.5.57, 9.0.37 - org.apache.tomcat:tomcat (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M7 - org.apache.tomcat:tomcat (Maven): affected from 10.0.0-M1; fixed in 10.0.0-M7 - org.apache.tomcat:tomcat (Maven): affected from 7.0.27; fixed in 7.0.105 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-2020-13935/ (Markdown: https://insights.sbomify.com/CVE-2020-13935/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2020-13935 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-13935 - OSV: https://osv.dev/vulnerability/CVE-2020-13935 --- From sbomify Insights: https://insights.sbomify.com/CVE-2020-13935/ Summaries are generated and may contain mistakes; the official description above is the record.