Is CVE-2021-43980 in the CISA KEV catalog?

No. CVE-2021-43980 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-43980?

CVE-2021-43980 has a CVSS v3 base score of 3.7 (LOW).

What is the EPSS score for CVE-2021-43980?

CVE-2021-43980 has an EPSS score of 1.75% (75th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-43980?

Upgrade tomcat9 on debian 11 to 9.0.43-2~deb11u4 or later.

CVE & CISA-KEV Catalog

CVE-2021-43980

LOWEPSS 75th pctl

3.7

CVSS v3

NVD

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.

CWE-362Race Condition

How to fix

Remediation Available

tomcat9Debian

Fixed in:9.0.43-2~deb11u4CVE-2021-43980

Fixed in:9.0.62-1CVE-2021-43980

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityNone

AvailabilityNone

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Exploit Intelligence

1.75%probability of exploitation in 30 days

75thpercentile

Elevated risk: more likely to be exploited than 75% of all known CVEs.

References

Vendor Advisory1

lists.apache.org

Third-Party Advisory3

Related Vulnerabilities

Other CWE-362 (Race Condition) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-6387	High	8.1	100%	-	Fix
CVE-2023-36884	High	7.5	99%	KEV + Ransom	Fix
CVE-2018-15473	Medium	5.3	99%	-	Fix
CVE-2024-27983	High	8.2	87%	-	Fix
CVE-2014-0226	Medium	6.8	86%	-	Fix
CVE-2016-5195	High	7.0	84%	KEV	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-05-21.