CVE-2021-21974

HIGHNVD 8.88.9▲
EchelonGraph scoreHIGH confidence

Score elevated to 8.9 because EPSS predicts 45% probability of exploitation within the next 30 days (98th percentile of EPSS-scored CVEs). NVD baseline CVSS 8.8 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, ghsa, nvd
Elevated
8.9EG
EchelonGraph verdictPlan mitigationSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 45%CVSS: 8.8Exploit: Elevated riskExposed services: Not assessed

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

OpenSLP as used in ESXi (7.0 before ESXi70U1c-17325551, 6.7 before ESXi670-202102401-SG, 6.5 before ESXi650-202102101-SG) has a heap-overflow vulnerability. A malicious actor residing within the same network segment as ESXi who has access to port 427 may be able to trigger the heap-overflow issue in OpenSLP service resulting in remote code execution.

CVSS v3
8.8
EG Score
8.9HIGHhigh 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
Severity89% × 45%
Exploitation45% × 40%
Automatability0% × 15%
CISA SSVC: Track at low, Track* at medium and Attend at high mission impact.
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
EPSS PROB
45%
EPSS %ILE
98th
KEV
Not listed

CISA SSVCTrack at low, Track* at medium and Attend at high mission impact.

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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

February 24, 2021

Last Modified

June 2, 2026

Advisory Details (3)

Auto-updated Jun 3, 2026
No patch confirmed yet.
generic

ZDI-21-250 | Zero Day Initiative

https://www.zerodayinitiative.com/advisories/ZDI-21-250/
generic

Support Content Notification - Support Portal - Broadcom support portal

https://www.vmware.com/security/advisories/VMSA-2021-0002.html
generic

Packet Storm

http://packetstormsecurity.com/files/162957/VMware-ESXi-OpenSLP-Heap-Overflow.html

Vendor Advisories for CVE-2021-21974(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 5× in last 7d / 28× 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 144 total refreshes for this CVE.

  1. 2026-10-03 14:22 UTCEPSS rescore
  2. 2026-10-03 14:22 UTCEPSS rescore
  3. 2026-10-01 19:46 UTCEPSS rescore
  4. 2026-09-30 15:30 UTCEG score recompute
  5. 2026-09-30 15:00 UTCEPSS rescore
  6. 2026-09-27 13:41 UTCEPSS rescore
  7. 2026-09-26 15:54 UTCEPSS rescore
  8. 2026-09-26 15:54 UTCEPSS rescore
  9. 2026-09-26 00:21 UTCEPSS rescore
  10. 2026-09-24 14:00 UTCEPSS rescore
  11. 2026-09-24 14:00 UTCEPSS rescore
  12. 2026-09-23 13:44 UTCEPSS rescore
  13. 2026-09-22 14:44 UTCEPSS rescore
  14. 2026-09-21 20:28 UTCEPSS rescore
  15. 2026-09-19 15:37 UTCEPSS rescore
  16. 2026-09-18 19:23 UTCEPSS rescore
  17. 2026-09-17 19:23 UTCEPSS rescore
  18. 2026-09-16 14:05 UTCEPSS rescore
  19. 2026-09-16 14:04 UTCEPSS rescore
  20. 2026-09-15 03:06 UTCEPSS rescore
  21. 2026-09-13 16:43 UTCEPSS rescore
  22. 2026-09-12 14:57 UTCEPSS rescore
  23. 2026-09-11 09:33 UTCEPSS rescore
  24. 2026-09-10 09:29 UTCEPSS rescore
  25. 2026-09-08 21:56 UTCEPSS rescore
Show 75 more
  1. 2026-09-07 15:58 UTCEPSS rescore
  2. 2026-09-06 13:44 UTCEPSS rescore
  3. 2026-09-06 13:44 UTCEPSS rescore
  4. 2026-09-05 15:25 UTCEPSS rescore
  5. 2026-09-04 13:57 UTCEPSS rescore
  6. 2026-09-02 14:08 UTCEPSS rescore
  7. 2026-09-01 13:50 UTCEPSS rescore
  8. 2026-09-01 03:32 UTCEPSS rescore
  9. 2026-08-30 19:14 UTCEPSS rescore
  10. 2026-08-30 01:19 UTCEPSS rescore
  11. 2026-08-28 21:37 UTCEPSS rescore
  12. 2026-08-27 14:22 UTCEPSS rescore
  13. 2026-08-26 14:42 UTCEPSS rescore
  14. 2026-08-25 13:45 UTCEPSS rescore
  15. 2026-08-23 00:16 UTCEPSS rescore
  16. 2026-08-21 23:46 UTCEPSS rescore
  17. 2026-08-20 22:52 UTCEPSS rescore
  18. 2026-08-19 17:01 UTCEPSS rescore
  19. 2026-08-18 13:45 UTCEPSS rescore
  20. 2026-08-17 13:43 UTCEPSS rescore
  21. 2026-08-16 02:11 UTCEPSS rescore
  22. 2026-08-15 01:27 UTCEPSS rescore
  23. 2026-08-13 21:57 UTCEPSS rescore
  24. 2026-08-12 13:47 UTCEPSS rescore
  25. 2026-08-11 13:38 UTCEPSS rescore
  26. 2026-08-09 13:43 UTCEPSS rescore
  27. 2026-08-07 16:23 UTCEPSS rescore
  28. 2026-08-06 13:43 UTCEPSS rescore
  29. 2026-08-03 10:32 UTCEPSS rescore
  30. 2026-08-01 04:12 UTCEPSS rescore
  31. 2026-07-30 16:25 UTCEPSS rescore
  32. 2026-07-30 01:27 UTCEPSS rescore
  33. 2026-07-30 01:27 UTCEPSS rescore
  34. 2026-07-26 14:52 UTCEPSS rescore
  35. 2026-07-25 14:15 UTCEPSS rescore
  36. 2026-07-24 14:15 UTCEPSS rescore
  37. 2026-07-23 14:15 UTCEPSS rescore
  38. 2026-07-23 01:57 UTCEG score recompute▲ 0.10
  39. 2026-07-22 22:43 UTCEG score recompute
  40. 2026-07-22 14:05 UTCEPSS rescore
  41. 2026-07-21 15:22 UTCEPSS rescore
  42. 2026-07-21 15:22 UTCEPSS rescore
  43. 2026-07-20 17:04 UTCEPSS rescore
  44. 2026-07-19 14:28 UTCEPSS rescore
  45. 2026-07-19 02:26 UTCEPSS rescore
  46. 2026-07-18 10:02 UTCEPSS rescore
  47. 2026-07-16 17:00 UTCEPSS rescore
  48. 2026-07-15 16:55 UTCEPSS rescore
  49. 2026-07-15 16:55 UTCEPSS rescore
  50. 2026-07-13 22:27 UTCEPSS rescore
  51. 2026-07-13 22:27 UTCEPSS rescore
  52. 2026-07-13 06:10 UTCEPSS rescore
  53. 2026-07-13 06:10 UTCEPSS rescore
  54. 2026-07-12 05:44 UTCEPSS rescore
  55. 2026-07-12 05:44 UTCEPSS rescore
  56. 2026-07-11 08:25 UTCEPSS rescore
  57. 2026-07-09 19:07 UTCEPSS rescore
  58. 2026-07-08 15:12 UTCEPSS rescore
  59. 2026-07-06 16:25 UTCEPSS rescore
  60. 2026-07-06 02:21 UTCEPSS rescore
  61. 2026-07-06 02:21 UTCEPSS rescore
  62. 2026-07-05 02:28 UTCEPSS rescore
  63. 2026-07-05 02:28 UTCEPSS rescore
  64. 2026-07-02 16:57 UTCEPSS rescore
  65. 2026-07-01 15:03 UTCEPSS rescore
  66. 2026-06-28 04:54 UTCEPSS rescore
  67. 2026-06-28 04:54 UTCEPSS rescore
  68. 2026-06-27 03:06 UTCEPSS rescore
  69. 2026-06-27 03:06 UTCEPSS rescore
  70. 2026-06-25 13:48 UTCEPSS rescore
  71. 2026-06-25 13:48 UTCEPSS rescore
  72. 2026-06-24 14:03 UTCEPSS rescore
  73. 2026-06-24 14:03 UTCEPSS rescore
  74. 2026-06-23 21:31 UTCEPSS rescore
  75. 2026-06-23 21:31 UTCEPSS rescore

Publicly available exploits

(5 references)

Working exploit code is in the public domain (5 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoChorizon3ai/CVE-2021-21974✓ verified
    First seen Mar 1, 2021

    ESXiArgs ransomware leveraged this OpenSLP heap-overflow at scale across unpatched ESXi hosts.

    Open source ↗
  • GitHub PoCAiyakami/CVE-2021-21974
    First seen Jul 8, 2026

    自研针对ESXI 堆栈溢出的CVE-2021-21974 POC，只支持项目给出的的目标和环境，用于学习和研究

    Open source ↗
  • GitHub PoCCYBERTHREATANALYSIS/ESXi-Ransomware-Scanner-mi
    First seen Feb 8, 2023

    ESXi EZ - A custom scanner that takes list of IPs either in JSON, CSV or individually and checks for infection CVE-2021-21974

    Open source ↗
  • GitHub PoCn2x4/Feb2023-CVE-2021-21974-OSINT
    First seen Feb 4, 2023

    Analysis of the ransom demands from Shodan results

    Open source ↗
  • GitHub PoCShadow0ps/CVE-2021-21974
    First seen May 25, 2021

    POC for CVE-2021-21974 VMWare ESXi RCE Exploit

    Open source ↗

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-21974?
CVE-2021-21974 is a high vulnerability published on February 24, 2021. OpenSLP as used in ESXi (7.0 before ESXi70U1c-17325551, 6.7 before ESXi670-202102401-SG, 6.5 before ESXi650-202102101-SG) has a heap-overflow vulnerability. A malicious actor residing within the same network segment as ESXi who has access to port 427 may be able to trigger the heap-overflow issue…
When was CVE-2021-21974 disclosed?
CVE-2021-21974 was first published on February 24, 2021, with the most recent update on June 2, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-21974 actively exploited?
CVE-2021-21974 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 45% probability of exploitation in the next 30 days (98th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-21974?
CVE-2021-21974 has a CVSS v3 base score of 8.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.9 (HIGH).
How do I remediate CVE-2021-21974?
No fix for CVE-2021-21974 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The vendor advisories EchelonGraph has for CVE-2021-21974 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2021-21974

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