CVE-2021-21295

MEDIUMNVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.9 under NVD CVSS v3. EPSS exploit probability: 19% (97th percentile of EPSS-scored CVEs). 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
Trending — 3 sources updated this weekElevated
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 19%CVSS: 5.9Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling. If a Content-Length header is present in the original HTTP/2 request, the field is not validated by Http2MultiplexHandler as it is propagated up. This is fine as long as the request is not proxied through as HTTP/1.1. If the request comes in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects (HttpRequest, HttpContent, etc.) via Http2StreamFrameToHttpObjectCodec and then sent up to the child channel's pipeline and proxied through a remote peer as HTTP/1.1 this may result in request smuggling. In a proxy case, users may assume the content-length is validated somehow, which is not the case. If the request is forwarded to a backend channel that is a HTTP/1.1 connection, the Content-Length now has meaning and needs to be checked. An attacker can smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1. For an example attack refer to the linked GitHub Advisory. Users are only affected if all of this is true: HTTP2MultiplexCodec or Http2FrameCodec is used, Http2StreamFrameToHttpObjectCodec is used to convert to HTTP/1.1 objects, and these HTTP/1.1 objects are forwarded to another remote peer. This has been patched in 4.1.60.Final As a workaround, the user can do the validation by themselves by implementing a custom ChannelInboundHandler that is put in the ChannelPipeline behind Http2StreamFrameToHttpObjectCodec.

CVSS v3
5.9
EG Score
5.9MEDIUMmedium confidence
EG Risk
58
EG Risk 58/100CISA 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
Severity59% × 45%
Exploitation40% × 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
19%
EPSS %ILE
97th
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

March 9, 2021

Last Modified

October 8, 2026

Advisory Details (10)

Auto-updated Oct 8, 2026
Patch available. Sources: github_pr, github_commit, github.
generic

Pony Mail

https://lists.apache.org/thread.html/r1908a34b9cc7120e5c19968a116ddbcffea5e9deb76c2be4fa461904%40%3Cdev.zookeeper.apache.org%3E
generic

Pony Mail

https://lists.apache.org/thread.html/r16c4b55ac82be72f28adad4f8061477e5f978199d5725691dcc82c24%40%3Ccommits.servicecomb.apache.org%3E
generic

Pony Mail

https://lists.apache.org/thread.html/r15f66ada9a5faf4bac69d9e7c4521cedfefa62df9509881603791969%40%3Cjira.kafka.apache.org%3E
generic

Pony Mail

https://lists.apache.org/thread.html/r0b09f3e31e004fe583f677f7afa46bd30110904576c13c5ac818ac2c%40%3Cissues.flink.apache.org%3E
generic

Pony Mail

https://lists.apache.org/thread.html/r04a3e0d9f53421fb946c60cc54762b7151dc692eb4e39970a7579052%40%3Ccommits.servicecomb.apache.org%3E
generic

Pony Mail

https://lists.apache.org/thread.html/r040a5e4d9cca2f98354b58a70b27099672276f66995c4e2e39545d0b%40%3Cissues.hbase.apache.org%3E
generic

Pony Mail

https://lists.apache.org/thread.html/r02e467123d45006a1dda20a38349e9c74c3a4b53e2e07be0939ecb3f%40%3Cdev.ranger.apache.org%3E
githubMentions a patch (unverified)

Possible request smuggling in HTTP/2 due missing validation · Advisory · netty/netty · GitHub

Affected: 4.1.60.Final

https://github.com/netty/netty/security/advisories/GHSA-wm47-8v5p-wjpj
github_commit Patch Available

commit 89c241e3b179 (netty/netty)

Patch available: netty/netty netty-4.1.132.Final (contains commit 89c241e3b179)

https://github.com/netty/netty/commit/89c241e3b1795ff257af4ad6eadc616cb2fb3dc4
github_pr Patch Available

core: add checks to chunked encoding for http/2

Patch available: Netflix/zuul v3.6.3 (PR #980 merged 2021-01-20)

https://github.com/Netflix/zuul/pull/980

Vendor Advisories for CVE-2021-21295(14)

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

Patch Availability(10)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntulibnetty-java (1:4.1.45-1ubuntu0.1~esm1) @ focal2026-10-08ubuntu
redhatcandlepin-0:4.1.13-1.el8sat2022-07-05redhat
redhatnetty2021-12-14redhat
redhatpatch2021-09-30redhat
redhateap7-netty-0:4.1.63-1.Final_redhat_00001.1.el7eap2021-09-23redhat
redhateap7-netty-0:4.1.63-1.Final_redhat_00001.1.el8eap2021-09-23redhat
redhateap7-yasson-0:1.0.9-1.redhat_00001.1.el8eap2021-05-19redhat
redhateap7-yasson-0:1.0.9-1.redhat_00001.1.el6eap2021-05-19redhat
redhateap7-yasson-0:1.0.9-1.redhat_00001.1.el7eap2021-05-19redhat
redhatqpid-proton-0:0.33.0-8.el82021-05-06redhat

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

(8 across 6 ecosystems)
Maven(3)
PackageVulnerable rangeFix by version rangeDependents
io.netty:netty3.10.0.Final ... 4.0.0.Alpha8 (71 versions)
  • every version on: no fix on record
—
io.netty:netty-codec-http24.1.0.Beta4 ... 4.1.9.Final (72 versions)
  • 4.0.0 up to 4.1.60.Final: fixed in 4.1.60.Final
—
org.jboss.netty:netty3.0.0.CR1 ... 3.2.9.Final (39 versions)
  • every version on: no fix on record
—
Debian:10(1)
PackageVulnerable rangeFix by version rangeDependents
netty1:4.1.33-1, 1:4.1.33-1+deb10u1
  • every version up to 1:4.1.33-1+deb10u2: fixed in 1:4.1.33-1+deb10u2
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
netty—
  • every version up to 1:4.1.48-3: fixed in 1:4.1.48-3
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
netty—
  • every version up to 1:4.1.48-3: fixed in 1:4.1.48-3
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
netty—
  • every version up to 1:4.1.48-3: fixed in 1:4.1.48-3
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
netty—
  • every version up to 1:4.1.48-3: fixed in 1:4.1.48-3
—

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 9× in last 7d / 33× 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 176 total refreshes for this CVE.

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

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Frequently asked(5)

What is CVE-2021-21295?
CVE-2021-21295 is a medium vulnerability published on March 9, 2021. Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling. If a…
When was CVE-2021-21295 disclosed?
CVE-2021-21295 was first published on March 9, 2021, 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-2021-21295 actively exploited?
CVE-2021-21295 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 19% probability of exploitation in the next 30 days (97th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-21295?
CVE-2021-21295 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2021-21295?
A fix for CVE-2021-21295 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-21295 are linked in the Vendor Advisories panel on this page.

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