How severe is CVE-2021-33037?

CVE-2021-33037 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-33037?

CVE-2021-33037 affects the following packages: org.apache.tomcat:tomcat (Maven), org.apache.tomcat:tomcat (Maven), org.apache.tomcat:tomcat (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-33037?

Update org.apache.tomcat:tomcat to 10.0.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33037 is resolved across your whole dependency graph.

How do I detect CVE-2021-33037 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.tomcat:tomcat, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-33037 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-33037 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-33037 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-33037?

CVE-2021-33037 has an EPSS (Exploit Prediction Scoring System) score of 74.7%, placing it in the 99th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-33037?

CVE-2021-33037 is classified as CWE-444 (CWE-444). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-33037 published, and has it been updated?

CVE-2021-33037 was published on July 12, 2021 and was last updated on October 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

MEDIUM severity

CVE-2021-33037 — tomcat

MEDIUMFix: apache/tomcat@05f9e8b

CVE-2021-33037 is a medium-severity (CVSS 5.3) CWE-444 vulnerability in org.apache.tomcat:tomcat. EPSS puts its 30-day exploitation probability at 74.7% (99th percentile). A fix is available for org.apache.tomcat:tomcat — see the affected versions and patch details below.

HTTP Request Smuggling in Apache Tomcat

Also known asBIT-tomcat-2021-33037GHSA-4vww-mc66-62m6

Published

Jul 12, 2021

Updated

Oct 10, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2021-33037.

EPSS Exploitation Probability

via FIRST.org ↗

74.7%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-33037 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

3 pkgs affected

☕org.apache.tomcat:tomcat☕org.apache.tomcat:tomcat☕org.apache.tomcat:tomcat

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.tomcat:tomcat`	≥ 10.0.0-M1&&< 10.0.7	10.0.7`org.apache.tomcat:tomcat:10.0.7`
☕Maven	`org.apache.tomcat:tomcat`	≥ 9.0.0-M1&&< 9.0.48	9.0.48`org.apache.tomcat:tomcat:9.0.48`
☕Maven	`org.apache.tomcat:tomcat`	≥ 8.5.0&&< 8.5.68	8.5.68`org.apache.tomcat:tomcat:8.5.68`

Affected Products

22 products · 42 configurations

Application

tomcatapache

≥ 8.5.0 && ≤ 10.0.6

range

Application

tomeeapache

1 version

8.0.6

debian linuxdebian

2 versions

9.010.0

Application

epolicy orchestratormcafee

< 5.10.0

1 version

5.10.0

Application

agile product lifecycle managementoracle

1 version

9.3.6

Application

communications cloud native core policyoracle

1 version

1.14.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.tomcat:tomcat, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.tomcat:tomcat to 10.0.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33037 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Red Hat OpenStack Platform's OpenDaylight will not be updated for this flaw because it was deprecated as of OpenStack Platform 14 and is only receiving security fixes for Critical flaws.

Product	Fixed in	Advisory
Red Hat Fuse 7.11	`tomcat`	RHSA-2022:5532
Red Hat JBoss Web Server 5	`tomcat`	RHSA-2021:4863
Red Hat JBoss Web Server 5.6 on RHEL 7	`jws5-tomcat-0:9.0.50-3.redhat_00004.1.el7jws`	RHSA-2021:4861
Red Hat Support for Spring Boot 2.5.10	`tomcat`	RHSA-2022:1179

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-33037 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVE-2021-33037 — tomcat

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Fixing This On Your OS

Frequently Asked Questions

Is CVE-2021-33037 in your dependencies?