CVE-2020-13943

MEDIUMNVD 4.36.4▲
EchelonGraph scoreHIGH confidence

Score elevated to 6.4 because EPSS predicts 55% probability of exploitation within the next 30 days (99th percentile of EPSS-scored CVEs). NVD baseline CVSS 4.3 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction (continuous uplift above 30%)
Sources: epss, nvd
Trending — 3 sources updated this weekElevated
6.4EG
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • 260 internet-facing services (distinct ip:port) on record running an affected version — derived from Shodan data (© Shodan); a patched service can stay counted while its port stays open
  • High exploitation likelihood — EPSS 55%
CISA-KEV: Not listedEPSS PROB: 55%CVSS: 4.3Exploit: Elevated riskExposed services: 260

A fix is available — apply it.

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.

Internet exposure · derived from Shodan data

260 internet-facing services (distinct ip:port) on record running a version that maps to CVE-2020-13943, in our KEV-Exposure radar’s Shodan-derived sample.

across 43 countries (Germany, China, United States, Brazil, France)top: tomcat
See the KEV-Exposure radar →Derived from Shodan data. Shodan data is owned by Shodan, which holds its copyright (© Shodan). EchelonGraph claims no ownership of it or copyright in it. Aggregate, host-redacted.

How it counts: every 12 hours, when Shodan query credits allow, the radar runs one Shodan query per tracked product, reads up to 100 ip:port services per query, and keeps a service when its banner version matches a CISA-KEV or high-EPSS CVE; a service is dropped when neither a search nor a Shodan InternetDB port re-check has refreshed it for 21 days. A re-check that finds the port still listed by Shodan InternetDB refreshes the service without re-reading the banner, so a patched service can stay counted while its port stays open. A count is a banner-version inference over a sample, not an exploit test and not an internet-wide census, and the unit is a service, not a machine: a machine answering on two ports counts twice.

CVSS v3
4.3
EG Score
6.4MEDIUMhigh confidence
EG Risk
66
EG Risk 66/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity64% × 45%
Exploitation55% × 40%
Automatability100% × 15%
CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
55%
EPSS %ILE
99th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

October 12, 2020

Last Modified

October 8, 2026

Advisory Details (4)

Auto-updated Oct 8, 2026
Patch available.
generic

Pony Mail

https://lists.apache.org/thread.html/r4a390027eb27e4550142fac6c8317cc684b157ae314d31514747f307%40%3Cannounce.tomcat.apache.org%3E
generic

[SECURITY] [DSA 4835-1] tomcat9 security update

https://www.debian.org/security/2021/dsa-4835
generic

NetApp Product Security

https://security.netapp.com/advisory/ntap-20201016-0007/
genericMentions a patch (unverified)

[SECURITY] [DLA 2407-1] tomcat8 security update

https://lists.debian.org/debian-lts-announce/2020/10/msg00019.html

Vendor Advisories for CVE-2020-13943(4)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(3)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntutomcat9-examples (9.0.31-1ubuntu0.2) @ focal2026-10-08ubuntu
redhattomcat2021-12-14redhat
redhatjws5-tomcat-native-0:1.2.25-3.redhat_3.el8jws2021-02-11redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(7 across 7 ecosystems)
Debian:10(1)
PackageVulnerable rangeFix by version rangeDependents
tomcat99.0.16-4 ... 9.0.31-1~deb10u2 (8 versions)
  • every version up to 9.0.31-1~deb10u3: fixed in 9.0.31-1~deb10u3
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
tomcat9—
  • every version up to 9.0.38-1: fixed in 9.0.38-1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
tomcat9—
  • every version up to 9.0.38-1: fixed in 9.0.38-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
tomcat9—
  • every version up to 9.0.38-1: fixed in 9.0.38-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
tomcat9—
  • every version up to 9.0.38-1: fixed in 9.0.38-1
—
Debian:9(1)
PackageVulnerable rangeFix by version rangeDependents
tomcat88.5.14-1 ... 8.5.54-0+deb9u3 (40 versions)
  • every version up to 8.5.54-0+deb9u4: fixed in 8.5.54-0+deb9u4
—
Maven(1)
PackageVulnerable rangeFix by version rangeDependents
org.apache.tomcat:tomcat-coyote8.5.0 ... 8.5.9 (46 versions)
  • 10.0.0-M1 up to 10.0.0-M8: fixed in 10.0.0-M8
  • 9.0.0-M1 up to 9.0.38: fixed in 9.0.38
  • 8.5.0 up to 8.5.58: fixed in 8.5.58
—

Additional Vendor Advisories

(1)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 8× in last 7d / 23× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 136 total refreshes for this CVE.

  1. 2026-10-09 20:03 UTCEPSS rescore
  2. 2026-10-08 22:29 UTCVendor advisory
  3. 2026-10-08 21:34 UTCEG score recompute▼ 0.20
  4. 2026-10-08 21:34 UTCVendor advisory
  5. 2026-10-08 16:38 UTCEPSS rescore
  6. 2026-10-07 23:43 UTCEPSS rescore
  7. 2026-10-06 15:13 UTCEPSS rescore
  8. 2026-10-04 23:18 UTCEPSS rescore
  9. 2026-09-30 15:11 UTCEG score recompute
  10. 2026-09-30 14:59 UTCEPSS rescore
  11. 2026-09-27 13:40 UTCEPSS rescore
  12. 2026-09-26 15:54 UTCEPSS rescore
  13. 2026-09-24 13:59 UTCEPSS rescore
  14. 2026-09-22 14:43 UTCEPSS rescore
  15. 2026-09-21 20:28 UTCEPSS rescore
  16. 2026-09-20 01:16 UTCOSV refresh
  17. 2026-09-18 19:23 UTCEPSS rescore
  18. 2026-09-17 19:22 UTCEPSS rescore
  19. 2026-09-16 14:04 UTCEPSS rescore
  20. 2026-09-16 14:04 UTCEPSS rescore
  21. 2026-09-15 03:06 UTCEPSS rescore
  22. 2026-09-12 14:56 UTCEPSS rescore
  23. 2026-09-11 14:48 UTCEPSS rescore
  24. 2026-09-06 13:44 UTCEPSS rescore
  25. 2026-09-05 15:24 UTCEPSS rescore
Show 75 more
  1. 2026-09-04 13:56 UTCEPSS rescore
  2. 2026-09-04 05:03 UTCEPSS rescore
  3. 2026-09-02 14:08 UTCEPSS rescore
  4. 2026-09-01 04:59 UTCOSV refresh
  5. 2026-08-30 19:14 UTCEPSS rescore
  6. 2026-08-28 21:37 UTCEPSS rescore
  7. 2026-08-26 14:42 UTCEPSS rescore
  8. 2026-08-25 13:45 UTCEPSS rescore
  9. 2026-08-20 22:51 UTCEPSS rescore
  10. 2026-08-19 17:00 UTCEPSS rescore
  11. 2026-08-17 13:43 UTCEPSS rescore
  12. 2026-08-16 14:52 UTCEPSS rescore
  13. 2026-08-16 02:11 UTCEPSS rescore
  14. 2026-08-15 04:07 UTCOSV refresh
  15. 2026-08-15 01:26 UTCEPSS rescore
  16. 2026-08-13 21:57 UTCEPSS rescore
  17. 2026-08-12 13:47 UTCEPSS rescore
  18. 2026-08-09 13:43 UTCEPSS rescore
  19. 2026-08-07 16:23 UTCEPSS rescore
  20. 2026-08-06 13:43 UTCEPSS rescore
  21. 2026-08-05 19:14 UTCEPSS rescore
  22. 2026-08-04 10:34 UTCEPSS rescore
  23. 2026-08-01 04:12 UTCEPSS rescore
  24. 2026-07-30 16:24 UTCEPSS rescore
  25. 2026-07-30 16:21 UTCOSV refresh
  26. 2026-07-30 01:27 UTCEPSS rescore
  27. 2026-07-28 15:32 UTCEPSS rescore
  28. 2026-07-26 14:51 UTCEPSS rescore
  29. 2026-07-25 14:14 UTCEPSS rescore
  30. 2026-07-24 14:14 UTCEPSS rescore
  31. 2026-07-23 14:15 UTCEPSS rescore
  32. 2026-07-23 14:15 UTCEPSS rescore
  33. 2026-07-23 01:49 UTCEG score recompute▲ 2.30
  34. 2026-07-22 22:34 UTCEG score recompute
  35. 2026-07-22 14:05 UTCEPSS rescore
  36. 2026-07-21 15:22 UTCEPSS rescore
  37. 2026-07-21 15:22 UTCEPSS rescore
  38. 2026-07-20 17:04 UTCEPSS rescore
  39. 2026-07-19 02:26 UTCEPSS rescore
  40. 2026-07-19 02:26 UTCEPSS rescore
  41. 2026-07-16 16:59 UTCEPSS rescore
  42. 2026-07-16 16:59 UTCEPSS rescore
  43. 2026-07-15 16:55 UTCEPSS rescore
  44. 2026-07-13 22:27 UTCEPSS rescore
  45. 2026-07-13 06:10 UTCEPSS rescore
  46. 2026-07-13 06:10 UTCEPSS rescore
  47. 2026-07-13 01:37 UTCOSV refresh
  48. 2026-07-12 05:44 UTCEPSS rescore
  49. 2026-07-11 08:24 UTCEPSS rescore
  50. 2026-07-09 19:06 UTCEPSS rescore
  51. 2026-07-07 13:43 UTCEPSS rescore
  52. 2026-07-05 02:27 UTCEPSS rescore
  53. 2026-07-01 15:03 UTCEPSS rescore
  54. 2026-07-01 15:03 UTCEPSS rescore
  55. 2026-06-30 23:20 UTCEPSS rescore
  56. 2026-06-30 23:20 UTCEPSS rescore
  57. 2026-06-28 14:05 UTCEPSS rescore
  58. 2026-06-28 04:54 UTCEPSS rescore
  59. 2026-06-28 04:54 UTCEPSS rescore
  60. 2026-06-27 03:06 UTCEPSS rescore
  61. 2026-06-25 13:47 UTCEPSS rescore
  62. 2026-06-25 13:47 UTCEPSS rescore
  63. 2026-06-24 10:50 UTCOSV refresh
  64. 2026-06-23 21:31 UTCEPSS rescore
  65. 2026-06-23 21:31 UTCEPSS rescore
  66. 2026-06-21 01:57 UTCEPSS rescore
  67. 2026-06-21 01:57 UTCEPSS rescore
  68. 2026-06-19 19:23 UTCEPSS rescore
  69. 2026-06-19 19:23 UTCEPSS rescore
  70. 2026-06-18 17:50 UTCEPSS rescore
  71. 2026-06-18 17:50 UTCEPSS rescore
  72. 2026-06-17 17:50 UTCEPSS rescore
  73. 2026-06-17 17:50 UTCEPSS rescore
  74. 2026-06-16 17:50 UTCEPSS rescore
  75. 2026-06-16 17:50 UTCEPSS rescore

Related CVEs(same product + same vendor)

Frequently asked(5)

What is CVE-2020-13943?
CVE-2020-13943 is a medium vulnerability published on October 12, 2020. 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…
When was CVE-2020-13943 disclosed?
CVE-2020-13943 was first published on October 12, 2020, with the most recent update on October 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-13943 actively exploited?
CVE-2020-13943 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 55% probability of exploitation in the next 30 days (99th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2020-13943?
CVE-2020-13943 has a CVSS v3 base score of 4.3 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 6.4 (MEDIUM).
How do I remediate CVE-2020-13943?
A fix for CVE-2020-13943 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2020-13943 are linked in the Vendor Advisories panel on this page.

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