What is CVE-2021-43980?

CVE-2021-43980 is a low-severity vulnerability in Apache Tomcat, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 3.7/10. Published 2022-09-28.

How severe is CVE-2021-43980?

Low severity. CVSS v3 base score is 3.7 out of 10.

Is CVE-2021-43980 known to be exploited?

4 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Apache Tomcat

CVE-2021-43980

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.

Vulnerability class: Race Condition

Published 2022-09-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.024 (83.2th percentile), scored 2026-10-02.

Low probability of exploitation in the next 30 days, but still tracked. 83rd percentile — 83.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.019 · newest: 0.024 · change: +0.005

Affected products

Apache Tomcat — versions 10.1.0
Apache Software Foundation Tomcat — versions 10.1.0-M1 to 10.1.0-M12, 10.0.0-M1 to 10.0.18, 9.0.0-M1 to 9.0.60
Debian Linux — versions 10.0, 11.0

Weakness classification (CWE)

CWE-362 — Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition)

Public proof-of-concept exploits

References

lists.apache.org/thread/3jjqbsp6j88b198x5rmg99b1qr8ht3g3 (Mailing List, Vendor Advisory)
www.openwall.com/lists/oss-security/2022/09/28/1 (mailing-list, Mailing List, Third Party Advisory)
lists.debian.org/debian-lts-announce/2022/10/msg00029.html (mailing-list, Mailing List, Third Party Advisory)
www.debian.org/security/2022/dsa-5265 (vendor-advisory, Third Party Advisory)

Frequently asked questions

What is CVE-2021-43980?: CVE-2021-43980 is a low-severity vulnerability in Apache Tomcat, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 3.7/10. Published 2022-09-28.
How severe is CVE-2021-43980?: Low severity. CVSS v3 base score is 3.7 out of 10.
Is CVE-2021-43980 known to be exploited?: 4 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.