# CVE-2021-42340: DoS via memory leak with WebSocket connections > A memory leak in Apache Tomcat's WebSocket handling can cause an OutOfMemoryError, leading to denial of service. - **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 Oct 2021 - **Updated:** 4 Aug 2024 - **Also known as:** BIT-tomcat-2021-42340, DEBIAN-CVE-2021-42340, DSA-5009-1, GHSA-wph7-x527-w3h5, OESA-2021-1413, RHBA-2022:8077 ## What is CVE-2021-42340? CVE-2021-42340 is a high-severity denial of service vulnerability in Apache Tomcat, published on 14 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description The fix for bug 63362 present in Apache Tomcat 10.1.0-M1 to 10.1.0-M5, 10.0.0-M1 to 10.0.11, 9.0.40 to 9.0.53 and 8.5.60 to 8.5.71 introduced a memory leak. The object introduced to collect metrics for HTTP upgrade connections was not released for WebSocket connections once the connection was closed. This created a memory leak that, over time, could lead to a denial of service via an OutOfMemoryError. Weakness: CWE-772 (Missing Release of Resource after Effective Lifetime) ## Which versions are affected by CVE-2021-42340? 9 open source packages ship an affected version, including org.apache.tomcat:tomcat and tomcat. It affects 18 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.apache.tomcat:tomcat` | Maven | From 10.0.0-M1 | 10.0.12 | | `org.apache.tomcat:tomcat` | Maven | From 10.0.0-M1 | 10.0.12 | | `org.apache.tomcat:tomcat` | Maven | From 10.1.0-M1 | 10.1.0-M6 | | `org.apache.tomcat:tomcat` | Maven | From 10.1.0-M1 | 10.1.0-M6 | | `org.apache.tomcat:tomcat` | Maven | From 8.5.60 | 8.5.72 | | `org.apache.tomcat:tomcat` | Maven | From 8.5.60 | 8.5.72 | | `org.apache.tomcat:tomcat` | Maven | From 9.0.40 | 9.0.54 | | `org.apache.tomcat:tomcat` | Maven | From 9.0.40 | 9.0.54 | | `tomcat` | Bitnami | From 8.5.60 | 8.5.72, 9.0.54, 10.0.12 | | `pki-servlet-4.0-api` | Red Hat:enterprise_linux:9::appstream | All versions | 1:9.0.50-1.el9 | | `pki-servlet-engine` | Red Hat:enterprise_linux:9::appstream | All versions | 1:9.0.50-1.el9 | Products: Apache Tomcat, Debian Debian Linux, Netapp Hci, Netapp Management Services for Element Software, Oracle Agile Engineering Data Management, Oracle Big Data Spatial and Graph, Oracle Communications Diameter Signaling Router, Oracle Hospitality Cruise Shipboard Property Management System, Oracle Managed File Transfer, Oracle Middleware Common Libraries and Tools, Oracle Payment Interface, Oracle Retail Customer Insights, Oracle Retail Data Extractor for Merchandising, Oracle Retail Eftlink, Oracle Retail Financial Integration, Oracle Retail Store Inventory Management, Oracle Sd-Wan Edge, Oracle Taleo Platform. ## How do I fix CVE-2021-42340? Upgrade org.apache.tomcat:tomcat to a fixed version for your release line: 10.0.12, 10.1.0-M6, 8.5.72 or 9.0.54. ## Is CVE-2021-42340 being exploited? There is no known exploitation of CVE-2021-42340 in the wild and no public exploit code. ## 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-2021-42340 and fix it if it is affected. What it is: CVE-2021-42340 is a high-severity denial of service vulnerability in Apache Tomcat, published on 14 Oct 2021. 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-2021-42340 in the wild and no public exploit code. Affected packages and fixed versions: - org.apache.tomcat:tomcat (Maven): affected from 10.0.0-M1; fixed in 10.0.12 - org.apache.tomcat:tomcat (Maven): affected from 10.0.0-M1; fixed in 10.0.12 - org.apache.tomcat:tomcat (Maven): affected from 10.1.0-M1; fixed in 10.1.0-M6 - org.apache.tomcat:tomcat (Maven): affected from 10.1.0-M1; fixed in 10.1.0-M6 - org.apache.tomcat:tomcat (Maven): affected from 8.5.60; fixed in 8.5.72 - org.apache.tomcat:tomcat (Maven): affected from 8.5.60; fixed in 8.5.72 - org.apache.tomcat:tomcat (Maven): affected from 9.0.40; fixed in 9.0.54 - org.apache.tomcat:tomcat (Maven): affected from 9.0.40; fixed in 9.0.54 - tomcat (Bitnami): affected from 8.5.60; fixed in 8.5.72, 9.0.54, 10.0.12 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-2021-42340/ (Markdown: https://insights.sbomify.com/CVE-2021-42340/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-42340 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-42340 - OSV: https://osv.dev/vulnerability/CVE-2021-42340 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-42340/ Summaries are generated and may contain mistakes; the official description above is the record.