CVE-2021-43797

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit probability: 0.4%, top 40% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 3%CVSS: 6.5Exploit: NoneExposed: 0

A fix is available — apply it.

Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. Netty prior to version 4.1.71.Final skips control chars when they are present at the beginning / end of the header name. It should instead fail fast as these are not allowed by the spec and could lead to HTTP request smuggling. Failing to do the validation might cause netty to "sanitize" header names before it forward these to another remote system when used as proxy. This remote system can't see the invalid usage anymore, and therefore does not do the validation itself. Users should upgrade to version 4.1.71.Final.

CVSS v3
6.5
EG Score
6.5(medium)
EPSS
84.1%
KEV
Not listed

Published

December 9, 2021

Last Modified

November 21, 2024

References (14)

Vendor Advisories for CVE-2021-43797(16)

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

Patch Availability(13)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulibnetty-java (1:4.1.48-4+deb11u1build0.22.04.1) @ jammy2026-05-26ubuntu
redhatnetty2022-11-03redhat
redhatrh-sso7-keycloak-0:18.0.3-1.redhat_00001.1.el7sso2022-11-03redhat
redhatrh-sso7-keycloak-0:18.0.3-1.redhat_00001.1.el8sso2022-11-03redhat
redhatrh-sso7-keycloak-0:18.0.3-1.redhat_00001.1.el9sso2022-11-03redhat
redhatrh-sso7-keycloak-0:15.0.8-1.redhat_00001.1.el8sso2022-10-04redhat
redhatrh-sso7-keycloak-0:15.0.8-1.redhat_00001.1.el7sso2022-10-04redhat
redhatcandlepin-0:4.1.13-1.el8sat2022-07-05redhat
redhateap7-netty-0:4.1.72-4.Final_redhat_00001.1.el8eap2022-06-06redhat
redhateap7-netty-0:4.1.72-4.Final_redhat_00001.1.el7eap2022-06-06redhat
redhatopenshift-logging/elasticsearch6-rhel8:v6.8.1-1572022-05-11redhat
redhatopenshift-logging/elasticsearch6-rhel8:v6.8.1-1562022-05-11redhat
redhatopenshift-logging/elasticsearch6-rhel8:v6.8.1-1592022-05-11redhat

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

(3 across 1 ecosystem)
Maven(3)
PackageVulnerable rangeFixed inDependents
io.netty:netty3.10.0.Final ... 4.0.0.Alpha8 (71 versions)——
io.netty:netty-codec-http4.0.0.Final ... 4.1.9.Final (144 versions)4.1.71.Final—
org.jboss.netty:netty3.0.0.CR1 ... 3.2.9.Final (39 versions)——

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(5)

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 11× in last 7d / 50× 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.

  1. 2026-07-11 08:25 UTCEPSS rescore
  2. 2026-07-11 08:25 UTCEPSS rescore
  3. 2026-07-09 19:07 UTCEPSS rescore
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  14. 2026-07-02 16:57 UTCEPSS rescore
  15. 2026-07-01 15:04 UTCEPSS rescore
  16. 2026-06-30 23:20 UTCEPSS rescore
  17. 2026-06-30 23:20 UTCEPSS rescore
  18. 2026-06-30 03:00 UTCOSV refresh
  19. 2026-06-29 14:04 UTCEPSS rescore
  20. 2026-06-28 14:05 UTCEPSS rescore
  21. 2026-06-28 04:54 UTCEPSS rescore
  22. 2026-06-28 04:54 UTCEPSS rescore
  23. 2026-06-27 03:06 UTCEPSS rescore
  24. 2026-06-27 03:06 UTCEPSS rescore
  25. 2026-06-25 13:48 UTCEPSS rescore
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  1. 2026-06-25 13:48 UTCEPSS rescore
  2. 2026-06-24 14:03 UTCEPSS rescore
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  4. 2026-06-23 21:31 UTCEPSS rescore
  5. 2026-06-23 21:31 UTCEPSS rescore
  6. 2026-06-22 14:24 UTCEPSS rescore
  7. 2026-06-21 14:55 UTCEPSS rescore
  8. 2026-06-21 01:58 UTCEPSS rescore
  9. 2026-06-21 01:58 UTCEPSS rescore
  10. 2026-06-19 19:24 UTCEPSS rescore
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  12. 2026-06-18 17:51 UTCEPSS rescore
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  19. 2026-06-15 17:46 UTCEPSS rescore
  20. 2026-06-14 23:15 UTCEPSS rescore
  21. 2026-06-14 23:15 UTCEPSS rescore
  22. 2026-06-13 22:58 UTCEPSS rescore
  23. 2026-06-13 22:58 UTCEPSS rescore
  24. 2026-06-12 23:10 UTCEPSS rescore
  25. 2026-06-12 15:10 UTCOSV refresh
  26. 2026-06-11 13:58 UTCEPSS rescore
  27. 2026-06-11 13:58 UTCEPSS rescore
  28. 2026-06-10 22:16 UTCEPSS rescore
  29. 2026-06-10 22:16 UTCEPSS rescore
  30. 2026-06-10 13:20 UTCEPSS rescore
  31. 2026-06-08 14:15 UTCEPSS rescore
  32. 2026-06-08 14:15 UTCEPSS rescore
  33. 2026-06-07 15:23 UTCEPSS rescore
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  35. 2026-06-06 13:46 UTCEPSS rescore
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  37. 2026-06-05 22:45 UTCEPSS rescore
  38. 2026-06-05 06:09 UTCEPSS rescore
  39. 2026-06-05 06:09 UTCEPSS rescore
  40. 2026-06-04 13:10 UTCEPSS rescore
  41. 2026-06-04 13:10 UTCEPSS rescore
  42. 2026-06-02 20:11 UTCEPSS rescore
  43. 2026-06-02 20:11 UTCEPSS rescore
  44. 2026-06-01 13:50 UTCEPSS rescore
  45. 2026-06-01 13:50 UTCEPSS rescore
  46. 2026-05-31 22:29 UTCEPSS rescore
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  48. 2026-05-31 00:15 UTCEPSS rescore
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  50. 2026-05-29 13:42 UTCEPSS rescore
  51. 2026-05-28 13:43 UTCEPSS rescore
  52. 2026-05-28 13:43 UTCEPSS rescore
  53. 2026-05-27 13:39 UTCEPSS rescore
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  55. 2026-05-26 13:42 UTCEPSS rescore
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  57. 2026-05-26 07:17 UTCEPSS rescore
  58. 2026-05-26 07:17 UTCEPSS rescore
  59. 2026-05-26 07:17 UTCEPSS rescore
  60. 2026-05-26 06:37 UTCEG score recompute
  61. 2026-05-26 06:37 UTCVendor advisory

Frequently asked(5)

What is CVE-2021-43797?
CVE-2021-43797 is a medium vulnerability published on December 9, 2021. Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. Netty prior to version 4.1.71.Final skips control chars when they are present at the beginning / end of the header name. It should instead fail fast…
When was CVE-2021-43797 disclosed?
CVE-2021-43797 was first published in the National Vulnerability Database on December 9, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-43797 actively exploited?
CVE-2021-43797 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 84.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-43797?
CVE-2021-43797 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2021-43797?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-43797, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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