CVE-2021-33037

CVE-2021-33037 is a medium-severity vulnerability in Apache Tomcat with a CVSS 3.x base score of 5.3. Its EPSS exploit-prediction score of 75% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-444.

Key facts

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.

Frequently asked questions

What is CVE-2021-33037?
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.
How severe is CVE-2021-33037?
CVE-2021-33037 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2021-33037 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 75% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-33037?
CVE-2021-33037 primarily affects Apache Tomcat. In total, 40 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-33037?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-33037 published?
CVE-2021-33037 was published on 2021-07-12 and last updated on 2026-06-17.

References

Affected products (40)

More vulnerabilities in Apache Tomcat

All CVEs affecting Apache Tomcat →

Other CWE-444 (HTTP Request/Response Smuggling) vulnerabilities

Browse all CWE-444 (HTTP Request/Response Smuggling) vulnerabilities →