CVE-2020-13943 is a medium-severity (CVSS 4.3) vulnerability in org.apache.tomcat:tomcat-coyote. EPSS puts its 30-day exploitation probability at 57.3% (99th percentile). A fix is available for org.apache.tomcat:tomcat-coyote — see the affected versions and patch details below.
Exposure of Sensitive Information to an Unauthorized Actor in Apache Tomcat
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-13943 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
org.apache.tomcat:tomcat-coyote☕org.apache.tomcat:tomcat-coyote☕org.apache.tomcat:tomcat-coyoteReal-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
If an HTTP/2 client connecting to Apache Tomcat 10.0.0-M1 to 10.0.0-M7, 9.0.0.M1 to 9.0.37 or 8.5.0 to 8.5.57 exceeded the agreed maximum number of concurrent streams for a connection (in violation of the HTTP/2 protocol), it was possible that a subsequent request made on that connection could contain HTTP headers - including HTTP/2 pseudo headers - from a previous request rather than the intended headers. This could lead to users seeing responses for unexpected resources.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.tomcat:tomcat-coyote | ≥ 10.0.0-M1&&< 10.0.0-M8 | 10.0.0-M8org.apache.tomcat:tomcat-coyote:10.0.0-M8 |
| ☕Maven | org.apache.tomcat:tomcat-coyote | ≥ 9.0.0-M1&&< 9.0.38 | 9.0.38org.apache.tomcat:tomcat-coyote:9.0.38 |
| ☕Maven | org.apache.tomcat:tomcat-coyote | ≥ 8.5.0&&< 8.5.58 | 8.5.58org.apache.tomcat:tomcat-coyote:8.5.58 |
Affected Products
tomcatapachedebian linuxdebianinstantis enterprisetrackoraclesd-wan edgeoracleDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.tomcat:tomcat-coyote, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.tomcat:tomcat-coyote to 10.0.0-M8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-13943 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 Hat Enterprise Linux 8's Identity Management is using an affected version of Tomcat bundled within PKI servlet engine, however HTTP/2 protocol is not supported by this component.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Fuse 7.10 | tomcat | RHSA-2021:5134 |
| Red Hat JBoss Web Server 5 | tomcat | RHSA-2021:0495 |
| Red Hat JBoss Web Server 5.4 on RHEL 7 | jws5-tomcat-0:9.0.36-9.redhat_8.1.el7jws | RHSA-2021:0494 |
| Red Hat Support for Spring Boot 2.4.9 | tomcat | RHSA-2021:4012 |
Frequently Asked Questions
Is CVE-2020-13943 in your dependencies?
Find it across Maven, including transitive dependencies.