CVE-2021-20236

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 9.8Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

CVSS v3
9.8
EG Score
9.8(medium)
EPSS
73.1%
KEV
Not listed

Published

May 28, 2021

Last Modified

November 21, 2024

Advisory Details (2)

Auto-updated May 30, 2026
Patch available. Sources: redhat, github.
github Patch Available

Stack overflow on server running PUB/XPUB socket (CURVE disabled) · Advisory · zeromq/libzmq · GitHub

https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8
redhat

1921976 – (CVE-2021-20236) CVE-2021-20236 zeromq: Stack overflow on server running PUB/XPUB socket

https://bugzilla.redhat.com/show_bug.cgi?id=1921976

Weakness Classification(2)

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

All Vendor Advisories

(1)

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 / 46× 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. 2026-07-16 17:00 UTCEPSS rescore
  2. 2026-07-15 16:55 UTCEPSS rescore
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  4. 2026-07-15 01:57 UTCEPSS rescore
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  12. 2026-07-09 19:07 UTCEPSS rescore
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  14. 2026-07-07 13:43 UTCEPSS rescore
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  20. 2026-07-04 06:29 UTCEPSS rescore
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  22. 2026-07-02 16:57 UTCEPSS rescore
  23. 2026-07-01 15:03 UTCEPSS rescore
  24. 2026-07-01 02:48 UTCOSV refresh
  25. 2026-06-30 23:20 UTCEPSS rescore
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  1. 2026-06-30 23:20 UTCEPSS rescore
  2. 2026-06-29 14:04 UTCEPSS rescore
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  4. 2026-06-28 14:05 UTCEPSS rescore
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  7. 2026-06-27 03:06 UTCEPSS rescore
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  9. 2026-06-25 13:48 UTCEPSS rescore
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  11. 2026-06-24 14:03 UTCEPSS rescore
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  15. 2026-06-21 14:54 UTCEPSS rescore
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  17. 2026-06-19 19:24 UTCEPSS rescore
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  19. 2026-06-18 17:51 UTCEPSS rescore
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  21. 2026-06-17 17:51 UTCEPSS rescore
  22. 2026-06-16 17:50 UTCEPSS rescore
  23. 2026-06-15 17:46 UTCEPSS rescore
  24. 2026-06-14 23:15 UTCEPSS rescore
  25. 2026-06-13 22:58 UTCEPSS rescore
  26. 2026-06-13 04:43 UTCOSV refresh
  27. 2026-06-12 23:10 UTCEPSS rescore
  28. 2026-06-12 23:10 UTCEPSS rescore
  29. 2026-06-11 13:58 UTCEPSS rescore
  30. 2026-06-10 22:16 UTCEPSS rescore
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  37. 2026-06-06 13:46 UTCEPSS rescore
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  40. 2026-06-05 22:45 UTCEPSS rescore
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  42. 2026-06-05 06:09 UTCEPSS rescore
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  45. 2026-06-04 13:10 UTCEPSS rescore
  46. 2026-06-02 20:11 UTCEPSS rescore
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  48. 2026-06-01 13:50 UTCEPSS rescore
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  50. 2026-05-31 22:29 UTCEPSS rescore
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  54. 2026-05-29 13:42 UTCEPSS rescore
  55. 2026-05-28 13:43 UTCEPSS rescore
  56. 2026-05-28 13:43 UTCEPSS rescore
  57. 2026-05-27 13:39 UTCEPSS rescore
  58. 2026-05-26 15:56 UTCEG score recompute
  59. 2026-05-26 15:56 UTCVendor advisory
  60. 2026-05-26 15:56 UTCGHSA enrichment
  61. 2026-05-26 13:42 UTCEPSS rescore
  62. 2026-05-26 13:42 UTCEPSS rescore
  63. 2026-05-26 07:17 UTCEPSS rescore
  64. 2026-05-26 07:17 UTCEPSS rescore
  65. 2026-05-24 16:49 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-20236?
CVE-2021-20236 is a critical vulnerability published on May 28, 2021. A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as…
When was CVE-2021-20236 disclosed?
CVE-2021-20236 was first published in the National Vulnerability Database on May 28, 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-2021-20236 actively exploited?
CVE-2021-20236 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 73.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-20236?
CVE-2021-20236 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-20236?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-20236, 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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