CVE-2009-0033 Apache Tomcat Denial of Service via Malformed Request Headers

What is CVE-2009-0033?

CVE-2009-0033 is a medium-severity denial of service vulnerability in Apache Tomcat, published on 5 Jun 2009. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Apache Tomcat 4.1.0 through 4.1.39, 5.5.0 through 5.5.27, and 6.0.0 through 6.0.18, when the Java AJP connector and mod_jk load balancing are used, allows remote attackers to cause a denial of service (application outage) via a crafted request with invalid headers, related to temporary blocking of connectors that have encountered errors, as demonstrated by an error involving a malformed HTTP Host header.

Weakness: CWE-20

Which versions are affected by CVE-2009-0033?

6 open source packages ship an affected version, including org.apache.tomcat:tomcat. It affects 1 product.

Products include Apache Tomcat.

How do I fix CVE-2009-0033?

Upgrade to a fixed version.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2009-0033 being exploited?

There is no known exploitation of CVE-2009-0033 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 GHSA-5cw4-ggx9-36vg.