CVE-2021-41816

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 34% 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
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 5%CVSS: 9.8Exploit: NoneExposed: 0

A fix is available — apply it.

CGI.escape_html in Ruby before 2.7.5 and 3.x before 3.0.3 has an integer overflow and resultant buffer overflow via a long string on platforms (such as Windows) where size_t and long have different numbers of bytes. This also affects the CGI gem before 0.3.1 for Ruby.

CVSS v3
9.8
EG Score
9.8(medium)
EPSS
91.0%
KEV
Not listed

Published

February 6, 2022

Last Modified

November 21, 2024

Advisory Details (6)

Auto-updated Jul 5, 2026
No patch confirmed yet.
generic

[SECURITY] Fedora 35 Update: ruby-3.0.4-153.fc35 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UTOJGS5IEFDK3UOO7IY4OTTFGHGLSWZF/
generic

[SECURITY] Fedora 34 Update: ruby-3.0.4-153.fc34 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IUXQCH6FRKANCVZO2Q7D2SQX33FP3KWN/
generic

CVE-2021-41816: Buffer Overrun in CGI.escape_html | Ruby

https://www.ruby-lang.org/en/news/2021/11/24/buffer-overrun-in-cgi-escape_html-cve-2021-41816/
generic

NetApp Product Security

https://security.netapp.com/advisory/ntap-20220303-0006/
generic

Ruby: Multiple vulnerabilities (GLSA 202401-27) — Gentoo security

https://security.gentoo.org/glsa/202401-27
generic

CVE-2021-41816

https://security-tracker.debian.org/tracker/CVE-2021-41816

Patch Availability(3)

Vendor / EcosystemFixed in / PatchReleasedSource
ubunturuby2.5-doc (2.5.1-1ubuntu1.11) @ bionic2026-05-26ubuntu
redhatrh-ruby30-ruby-0:3.0.4-149.el72022-10-11redhat
redhatrh-ruby27-ruby-0:2.7.6-131.el72022-10-11redhat

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

(1 across 1 ecosystem)
RubyGems(1)
PackageVulnerable rangeFixed inDependents
cgi0.1.00.1.0.1—

Weakness Classification(1)

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

All Vendor Advisories

(3)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 11× in last 7d / 49× 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 102 total refreshes for this CVE.

  1. 2026-07-22 14:06 UTCEPSS rescore
  2. 2026-07-21 15:22 UTCEPSS rescore
  3. 2026-07-21 15:22 UTCEPSS rescore
  4. 2026-07-20 17:05 UTCEPSS rescore
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  7. 2026-07-18 10:02 UTCEPSS rescore
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  9. 2026-07-18 01:29 UTCOSV refresh
  10. 2026-07-16 17:00 UTCEPSS rescore
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  12. 2026-07-15 16:55 UTCEPSS rescore
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  24. 2026-07-07 13:43 UTCEPSS rescore
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  1. 2026-07-06 16:25 UTCEPSS rescore
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  8. 2026-07-02 16:57 UTCEPSS rescore
  9. 2026-07-01 15:04 UTCEPSS rescore
  10. 2026-06-30 23:20 UTCEPSS rescore
  11. 2026-06-30 23:20 UTCEPSS rescore
  12. 2026-06-29 21:32 UTCOSV refresh
  13. 2026-06-29 14:04 UTCEPSS rescore
  14. 2026-06-28 14:05 UTCEPSS rescore
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  17. 2026-06-27 03:06 UTCEPSS rescore
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  19. 2026-06-25 13:48 UTCEPSS rescore
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  21. 2026-06-24 14:03 UTCEPSS rescore
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  23. 2026-06-23 21:31 UTCEPSS rescore
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  25. 2026-06-21 14:55 UTCEPSS rescore
  26. 2026-06-21 01:58 UTCEPSS rescore
  27. 2026-06-21 01:58 UTCEPSS rescore
  28. 2026-06-18 17:51 UTCEPSS rescore
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  30. 2026-06-17 17:51 UTCEPSS rescore
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  35. 2026-06-15 17:46 UTCEPSS rescore
  36. 2026-06-14 23:15 UTCEPSS rescore
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  38. 2026-06-13 22:58 UTCEPSS rescore
  39. 2026-06-13 22:58 UTCEPSS rescore
  40. 2026-06-12 23:10 UTCEPSS rescore
  41. 2026-06-12 09:40 UTCOSV refresh
  42. 2026-06-11 13:58 UTCEPSS rescore
  43. 2026-06-11 13:58 UTCEPSS rescore
  44. 2026-06-10 22:16 UTCEPSS rescore
  45. 2026-06-10 22:16 UTCEPSS rescore
  46. 2026-06-10 13:20 UTCEPSS rescore
  47. 2026-06-08 14:15 UTCEPSS rescore
  48. 2026-06-08 14:15 UTCEPSS rescore
  49. 2026-06-07 15:23 UTCEPSS rescore
  50. 2026-06-07 15:23 UTCEPSS rescore
  51. 2026-06-06 13:46 UTCEPSS rescore
  52. 2026-06-06 13:46 UTCEPSS rescore
  53. 2026-06-05 22:45 UTCEPSS rescore
  54. 2026-06-05 06:09 UTCEPSS rescore
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  58. 2026-06-02 20:11 UTCEPSS rescore
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  60. 2026-06-01 13:50 UTCEPSS rescore
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  62. 2026-05-31 22:29 UTCEPSS rescore
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  73. 2026-05-26 07:17 UTCEPSS rescore
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  75. 2026-05-26 07:17 UTCEPSS rescore

Frequently asked(5)

What is CVE-2021-41816?
CVE-2021-41816 is a critical vulnerability published on February 6, 2022. CGI.escapehtml in Ruby before 2.7.5 and 3.x before 3.0.3 has an integer overflow and resultant buffer overflow via a long string on platforms (such as Windows) where sizet and long have different numbers of bytes. This also affects the CGI gem before 0.3.1 for Ruby.
When was CVE-2021-41816 disclosed?
CVE-2021-41816 was first published in the National Vulnerability Database on February 6, 2022, 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-2021-41816 actively exploited?
CVE-2021-41816 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 91.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-41816?
CVE-2021-41816 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-41816?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-41816, 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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