Summary
Apache Tomcat 10.0.0-M1 to 10.0.6, 9.0.0.M1 to 9.0.46 and 8.5.0 to 8.5.66 did not correctly parse the HTTP transfer-encoding request header in some circumstances leading to the possibility to request smuggling when used with a reverse proxy. Specifically: - Tomcat incorrectly ignored the transfer encoding header if the client declared it would only accept an HTTP/1.0 response; - Tomcat honoured the identify encoding; and - Tomcat did not ensure that, if present, the chunked encoding was the final encoding.
Impact
CVE-2021-33037 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (10.0.7, 9.0.48, 8.5.68); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
org.apache.tomcat:tomcat to 10.0.7 or later; org.apache.tomcat:tomcat to 9.0.48 or later; org.apache.tomcat:tomcat to 8.5.68 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2021-33037? CVE-2021-33037 is a medium-severity security vulnerability in org.apache.tomcat:tomcat (maven), affecting versions >= 10.0.0-M1, < 10.0.7. It is fixed in 10.0.7, 9.0.48, 8.5.68.
- How severe is CVE-2021-33037? CVE-2021-33037 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.apache.tomcat:tomcat are affected by CVE-2021-33037? org.apache.tomcat:tomcat (maven) versions >= 10.0.0-M1, < 10.0.7 is affected.
- Is there a fix for CVE-2021-33037? Yes. CVE-2021-33037 is fixed in 10.0.7, 9.0.48, 8.5.68. Upgrade to this version or later.
- Is CVE-2021-33037 exploitable, and should I be worried? Whether CVE-2021-33037 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-33037 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-33037?
- Upgrade
org.apache.tomcat:tomcatto 10.0.7 or later - Upgrade
org.apache.tomcat:tomcatto 9.0.48 or later - Upgrade
org.apache.tomcat:tomcatto 8.5.68 or later
- Upgrade