CVE-2021-43980 is a low-severity (CVSS 3.7) CWE-362 vulnerability in org.apache.tomcat:tomcat. A fix is available for org.apache.tomcat:tomcat — see the affected versions and patch details below.
Apache Tomcat Race Condition vulnerability
Exploitation Status
No confirmed exploitation observed yet
- 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-2021-43980.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
org.apache.tomcat:tomcat☕org.apache.tomcat:tomcat☕org.apache.tomcat:tomcat☕org.apache.tomcat:tomcatReal-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
The simplified implementation of blocking reads and writes introduced in Tomcat 10 and back-ported to Tomcat 9.0.47 onwards exposed a long standing (but extremely hard to trigger) concurrency bug in Apache Tomcat 10.1.0 to 10.1.0-M12, 10.0.0-M1 to 10.0.18, 9.0.0-M1 to 9.0.60 and 8.5.0 to 8.5.77 that could cause client connections to share an Http11Processor instance resulting in responses, or part responses, to be received by the wrong client.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.tomcat:tomcat | ≥ 8.5.0&&< 8.5.78 | 8.5.78org.apache.tomcat:tomcat:8.5.78 |
| ☕Maven | org.apache.tomcat:tomcat | ≥ 9.0.0-M1&&< 9.0.62 | 9.0.62org.apache.tomcat:tomcat:9.0.62 |
| ☕Maven | org.apache.tomcat:tomcat | ≥ 10.0.0-M1&&< 10.0.20 | 10.0.20org.apache.tomcat:tomcat:10.0.20 |
| ☕Maven | org.apache.tomcat:tomcat | ≥ 10.1.0-M1&&< 10.1.0-M14 | 10.1.0-M14org.apache.tomcat:tomcat:10.1.0-M14 |
Affected Products
tomcatapachedebian linuxdebianDetection & 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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.tomcat:tomcat to 8.5.78 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43980 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 Satellite does not include the affected Apache Tomcat, however, Tomcat is shipped with Red Hat Enterprise Linux and consumed by the Candlepin component of Satellite. Red Hat Satellite users are therefore advised to check the impact state of Red Hat Enterprise Linux, since any necessary fixes will be…
| Product | Fixed in | Advisory |
|---|---|---|
| JWS 5.7.0 | see advisory | RHSA-2022:7273 |
| Red Hat JBoss Web Server 5.7 on RHEL 7 | jws5-ecj-0:4.20.0-1.redhat_00002.1.el7jws | RHSA-2022:7272 |
Frequently Asked Questions
Is CVE-2021-43980 in your dependencies?
Find it across Maven, including transitive dependencies.