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
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 2%CVSS: 9.8Exploit: None knownExposed: 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)
EG Risk
49(Track)
EG Risk 49/100SSVC: Track

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
Severity98% × 45%
Exploitation2% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
2%
EPSS %ILE
73%
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 9× in last 7d / 42× 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 104 total refreshes for this CVE.

  1. 2026-07-26 14:52 UTCEPSS rescore
  2. 2026-07-25 14:15 UTCEPSS rescore
  3. 2026-07-24 14:15 UTCEPSS rescore
  4. 2026-07-23 14:15 UTCEPSS rescore
  5. 2026-07-23 01:56 UTCEG score recompute
  6. 2026-07-22 22:43 UTCEG score recompute
  7. 2026-07-22 14:05 UTCEPSS rescore
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  13. 2026-07-18 19:29 UTCOSV refresh
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  1. 2026-07-09 19:07 UTCEPSS rescore
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  11. 2026-07-02 16:57 UTCEPSS rescore
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  13. 2026-07-01 02:48 UTCOSV refresh
  14. 2026-06-30 23:20 UTCEPSS rescore
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  23. 2026-06-25 13:48 UTCEPSS rescore
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  25. 2026-06-24 14:03 UTCEPSS rescore
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  27. 2026-06-23 21:31 UTCEPSS rescore
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  29. 2026-06-21 14:54 UTCEPSS rescore
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  31. 2026-06-19 19:24 UTCEPSS rescore
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  38. 2026-06-14 23:15 UTCEPSS rescore
  39. 2026-06-13 22:58 UTCEPSS rescore
  40. 2026-06-13 04:43 UTCOSV refresh
  41. 2026-06-12 23:10 UTCEPSS rescore
  42. 2026-06-12 23:10 UTCEPSS rescore
  43. 2026-06-11 13:58 UTCEPSS rescore
  44. 2026-06-10 22:16 UTCEPSS rescore
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  46. 2026-06-10 13:20 UTCEPSS rescore
  47. 2026-06-08 14:15 UTCEPSS rescore
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  49. 2026-06-07 15:23 UTCEPSS rescore
  50. 2026-06-07 15:23 UTCEPSS rescore
  51. 2026-06-06 13:46 UTCEPSS rescore
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  64. 2026-05-31 22:29 UTCEPSS rescore
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  68. 2026-05-29 13:42 UTCEPSS rescore
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  71. 2026-05-27 13:39 UTCEPSS rescore
  72. 2026-05-26 15:56 UTCEG score recompute
  73. 2026-05-26 15:56 UTCVendor advisory
  74. 2026-05-26 15:56 UTCGHSA enrichment
  75. 2026-05-26 13:42 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

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 2% probability of exploitation in the next 30 days, which ranks it in the top 26.7% of all scored CVEs.
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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