CVE-2020-13943

CVE-2020-13943 is a medium-severity vulnerability in Apache Tomcat with a CVSS 3.x base score of 4.3. Its EPSS exploit-prediction score of 57% places it in the 99th percentile, indicating an elevated likelihood of exploitation.

Key facts

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.

Frequently asked questions

What is CVE-2020-13943?
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.
How severe is CVE-2020-13943?
CVE-2020-13943 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2020-13943 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 57% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-13943?
CVE-2020-13943 primarily affects Apache Tomcat. In total, 131 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-13943?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2020-13943 published?
CVE-2020-13943 was published on 2020-10-12 and last updated on 2026-06-17.

References

Affected products (131)

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