CVE-2021-33037 Incorrect Transfer-Encoding handling with HTTP/1.0

What is CVE-2021-33037?

CVE-2021-33037 is a medium-severity vulnerability in Apache Tomcat, published on 12 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-444

Which versions are affected by CVE-2021-33037?

7 open source packages ship an affected version, including org.apache.tomcat:tomcat and tomcat. It affects 22 products.

Products include Apache Tomcat, Apache Tomee, Debian Debian Linux, Mcafee Epolicy Orchestrator, Oracle Agile Product Lifecycle Management, Oracle Communications Cloud Native Core Policy and 16 more.

How do I fix CVE-2021-33037?

Upgrade org.apache.tomcat:tomcat to a fixed version for your release line: 10.0.7, 8.5.68 or 9.0.48.

Is CVE-2021-33037 being exploited?

There is no known exploitation of CVE-2021-33037 in the wild and no public exploit code.

Other vulnerabilities in Apache Tomcat

• CVE-2025-24813 Apache Tomcat Path Equivalence Exploited Critical 10.0
• CVE-2016-8735 Apache Tomcat Remote Code Execution Exploited Critical 9.8
• CVE-2017-12617 Apache Tomcat Remote Code Execution Exploited High 8.1
• CVE-2017-12615 Apache Tomcat on Windows Remote Code Execution Exploited High 8.1
• CVE-2026-34486 Apache Tomcat Missing Encryption of Sensitive Data Exploited High 7.5

All Apache Tomcat vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-tomcat-2021-33037, DEBIAN-CVE-2021-33037, GHSA-4vww-mc66-62m6, OESA-2021-1275, UBUNTU-CVE-2021-33037.