---
id: CVE-2020-13943
title: >-
  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 possibl…
summary: >-
  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 possibl…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N'
vendor: apache
product: tomcat
affected:
  - tomcat = 8.5.0
  - tomcat = 8.5.1
  - tomcat = 8.5.2
  - tomcat = 8.5.3
  - tomcat = 8.5.4
  - tomcat = 8.5.5
  - tomcat = 8.5.6
  - tomcat = 8.5.7
  - tomcat = 8.5.8
  - tomcat = 8.5.9
  - tomcat = 8.5.10
  - tomcat = 8.5.11
  - tomcat = 8.5.12
  - tomcat = 8.5.13
  - tomcat = 8.5.14
  - tomcat = 8.5.15
  - tomcat = 8.5.16
  - tomcat = 8.5.17
  - tomcat = 8.5.18
  - tomcat = 8.5.19
  - tomcat = 8.5.20
  - tomcat = 8.5.21
  - tomcat = 8.5.22
  - tomcat = 8.5.23
  - tomcat = 8.5.24
  - tomcat = 8.5.25
  - tomcat = 8.5.26
  - tomcat = 8.5.27
  - tomcat = 8.5.28
  - tomcat = 8.5.29
  - tomcat = 8.5.30
  - tomcat = 8.5.31
  - tomcat = 8.5.32
  - tomcat = 8.5.33
  - tomcat = 8.5.34
  - tomcat = 8.5.35
  - tomcat = 8.5.36
  - tomcat = 8.5.37
  - tomcat = 8.5.38
  - tomcat = 8.5.39
  - tomcat = 8.5.40
  - tomcat = 8.5.41
  - tomcat = 8.5.42
  - tomcat = 8.5.43
  - tomcat = 8.5.44
  - tomcat = 8.5.45
  - tomcat = 8.5.46
  - tomcat = 8.5.47
  - tomcat = 8.5.48
  - tomcat = 8.5.49
  - tomcat = 8.5.50
  - tomcat = 8.5.51
  - tomcat = 8.5.52
  - tomcat = 8.5.53
  - tomcat = 8.5.54
  - tomcat = 8.5.55
  - tomcat = 8.5.56
  - tomcat = 8.5.57
  - tomcat = 9.0.0
  - tomcat = 9.0.1
  - tomcat = 9.0.2
  - tomcat = 9.0.3
  - tomcat = 9.0.4
  - tomcat = 9.0.5
  - tomcat = 9.0.6
  - tomcat = 9.0.7
  - tomcat = 9.0.8
  - tomcat = 9.0.9
  - tomcat = 9.0.10
  - tomcat = 9.0.11
  - tomcat = 9.0.12
  - tomcat = 9.0.13
  - tomcat = 9.0.14
  - tomcat = 9.0.15
  - tomcat = 9.0.16
  - tomcat = 9.0.17
  - tomcat = 9.0.18
  - tomcat = 9.0.19
  - tomcat = 9.0.20
  - tomcat = 9.0.21
  - tomcat = 9.0.22
  - tomcat = 9.0.23
  - tomcat = 9.0.24
  - tomcat = 9.0.25
  - tomcat = 9.0.26
  - tomcat = 9.0.27
  - tomcat = 9.0.28
  - tomcat = 9.0.29
  - tomcat = 9.0.30
  - tomcat = 9.0.31
  - tomcat = 9.0.32
  - tomcat = 9.0.33
  - tomcat = 9.0.34
  - tomcat = 9.0.35
  - tomcat = 9.0.36
  - tomcat = 9.0.37
  - tomcat = 10.0.0
  - debian_linux = 9.0
  - debian_linux = 10.0
  - instantis_enterprisetrack = 17.1
published: '2020-10-12'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T22:16:56.900'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-13943'
references:
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00002.html'
    label: security@apache.org
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00021.html'
    label: security@apache.org
  - url: >-
      https://lists.apache.org/thread.html/r4a390027eb27e4550142fac6c8317cc684b157ae314d31514747f307%40%3Cannounce.tomcat.apache.org%3E
    label: security@apache.org
  - url: 'https://lists.debian.org/debian-lts-announce/2020/10/msg00019.html'
    label: security@apache.org
  - url: 'https://security.netapp.com/advisory/ntap-20201016-0007/'
    label: security@apache.org
  - url: 'https://www.debian.org/security/2021/dsa-4835'
    label: security@apache.org
  - url: 'https://www.oracle.com/security-alerts/cpuApr2021.html'
    label: security@apache.org
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00002.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00021.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.apache.org/thread.html/r4a390027eb27e4550142fac6c8317cc684b157ae314d31514747f307%40%3Cannounce.tomcat.apache.org%3E
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2020/10/msg00019.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://security.netapp.com/advisory/ntap-20201016-0007/'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://www.debian.org/security/2021/dsa-4835'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://www.oracle.com/security-alerts/cpuApr2021.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.54966
epssPercentile: 0.99005
ingestedAt: '2026-10-08T23:16:47.309Z'
---

## Overview

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

- `tomcat = 8.5.0`
- `tomcat = 8.5.1`
- `tomcat = 8.5.2`
- `tomcat = 8.5.3`
- `tomcat = 8.5.4`
- `tomcat = 8.5.5`
- `tomcat = 8.5.6`
- `tomcat = 8.5.7`
- `tomcat = 8.5.8`
- `tomcat = 8.5.9`
- `tomcat = 8.5.10`
- `tomcat = 8.5.11`
- `tomcat = 8.5.12`
- `tomcat = 8.5.13`
- `tomcat = 8.5.14`
- `tomcat = 8.5.15`
- `tomcat = 8.5.16`
- `tomcat = 8.5.17`
- `tomcat = 8.5.18`
- `tomcat = 8.5.19`
- `tomcat = 8.5.20`
- `tomcat = 8.5.21`
- `tomcat = 8.5.22`
- `tomcat = 8.5.23`
- `tomcat = 8.5.24`
- `tomcat = 8.5.25`
- `tomcat = 8.5.26`
- `tomcat = 8.5.27`
- `tomcat = 8.5.28`
- `tomcat = 8.5.29`
- `tomcat = 8.5.30`
- `tomcat = 8.5.31`
- `tomcat = 8.5.32`
- `tomcat = 8.5.33`
- `tomcat = 8.5.34`
- `tomcat = 8.5.35`
- `tomcat = 8.5.36`
- `tomcat = 8.5.37`
- `tomcat = 8.5.38`
- `tomcat = 8.5.39`
- `tomcat = 8.5.40`
- `tomcat = 8.5.41`
- `tomcat = 8.5.42`
- `tomcat = 8.5.43`
- `tomcat = 8.5.44`
- `tomcat = 8.5.45`
- `tomcat = 8.5.46`
- `tomcat = 8.5.47`
- `tomcat = 8.5.48`
- `tomcat = 8.5.49`
- `tomcat = 8.5.50`
- `tomcat = 8.5.51`
- `tomcat = 8.5.52`
- `tomcat = 8.5.53`
- `tomcat = 8.5.54`
- `tomcat = 8.5.55`
- `tomcat = 8.5.56`
- `tomcat = 8.5.57`
- `tomcat = 9.0.0`
- `tomcat = 9.0.1`
- `tomcat = 9.0.2`
- `tomcat = 9.0.3`
- `tomcat = 9.0.4`
- `tomcat = 9.0.5`
- `tomcat = 9.0.6`
- `tomcat = 9.0.7`
- `tomcat = 9.0.8`
- `tomcat = 9.0.9`
- `tomcat = 9.0.10`
- `tomcat = 9.0.11`
- `tomcat = 9.0.12`
- `tomcat = 9.0.13`
- `tomcat = 9.0.14`
- `tomcat = 9.0.15`
- `tomcat = 9.0.16`
- `tomcat = 9.0.17`
- `tomcat = 9.0.18`
- `tomcat = 9.0.19`
- `tomcat = 9.0.20`
- `tomcat = 9.0.21`
- `tomcat = 9.0.22`
- `tomcat = 9.0.23`
- `tomcat = 9.0.24`
- `tomcat = 9.0.25`
- `tomcat = 9.0.26`
- `tomcat = 9.0.27`
- `tomcat = 9.0.28`
- `tomcat = 9.0.29`
- `tomcat = 9.0.30`
- `tomcat = 9.0.31`
- `tomcat = 9.0.32`
- `tomcat = 9.0.33`
- `tomcat = 9.0.34`
- `tomcat = 9.0.35`
- `tomcat = 9.0.36`
- `tomcat = 9.0.37`
- `tomcat = 10.0.0`
- `debian_linux = 9.0`
- `debian_linux = 10.0`
- `instantis_enterprisetrack = 17.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.