CVE-2021-20220

MEDIUMNVD 4.84.8—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.8 under NVD CVSS v3. EPSS exploit probability: 1.2% (67th 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
4.8EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 1.2%CVSS: 4.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

A flaw was found in Undertow. A regression in the fix for CVE-2020-10687 was found. HTTP request smuggling related to CVE-2017-2666 is possible against HTTP/1.x and HTTP/2 due to permitting invalid characters in an HTTP request. This flaw allows an attacker to poison a web-cache, perform an XSS attack, or obtain sensitive information from request other than their own. The highest threat from this vulnerability is to data confidentiality and integrity.

CVSS v3
4.8
EG Score
4.8MEDIUMmedium confidence
EG Risk
27
EG Risk 27/100CISA 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
Severity48% × 45%
Exploitation1% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track or 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
1.2%
EPSS %ILE
67th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track or 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 (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). 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

February 23, 2021

Last Modified

November 21, 2024

References (4)

Vendor Advisories for CVE-2021-20220(2)

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

Patch Availability(4)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatwildfly-undertow2021-07-15redhat
redhateap7-wildfly-naming-client-0:1.0.14-1.Final_redhat_00001.1.el8eap2021-03-16redhat
redhateap7-wildfly-naming-client-0:1.0.14-1.Final_redhat_00001.1.el7eap2021-03-16redhat
redhateap7-wildfly-naming-client-0:1.0.14-1.Final_redhat_00001.1.el6eap2021-03-16redhat

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

(2 across 2 ecosystems)
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
undertow1.3.11-1 ... 2.1.3-1 (35 versions)
  • every version up to 2.2.0-1: fixed in 2.2.0-1
—
Maven(1)
PackageVulnerable rangeFix by version rangeDependents
io.undertow:undertow-core1.0.0.Alpha1 ... 2.0.9.Final (250 versions)
  • 2.1.0 up to 2.1.6: fixed in 2.1.6
  • every version up to 2.0.34: fixed in 2.0.34
—

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 8× 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 184 total refreshes for this CVE.

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

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Frequently asked(5)

What is CVE-2021-20220?
CVE-2021-20220 is a medium vulnerability published on February 23, 2021. A flaw was found in Undertow. A regression in the fix for CVE-2020-10687 was found. HTTP request smuggling related to CVE-2017-2666 is possible against HTTP/1.x and HTTP/2 due to permitting invalid characters in an HTTP request. This flaw allows an attacker to poison a web-cache, perform an XSS…
When was CVE-2021-20220 disclosed?
CVE-2021-20220 was first published on February 23, 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-2021-20220 actively exploited?
CVE-2021-20220 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.2% probability of exploitation in the next 30 days (67th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-20220?
CVE-2021-20220 has a CVSS v3 base score of 4.8 (NVD).
How do I remediate CVE-2021-20220?
A fix for CVE-2021-20220 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-20220 are linked in the Vendor Advisories panel on this page.

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