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 (top 1.3% of all 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 a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 45%CVSS: 8.8Exploit: Elevated riskExposed: 0

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

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
8.9(high)
EG Risk
58(Track*)
EG Risk 58/100SSVC: 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
Severity89% × 45%
Exploitation45% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
45%
EPSS %ILE
99%
KEV
Not listed

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 6× in last 7d / 23× 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 103 total refreshes for this CVE.

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

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 in the National Vulnerability Database 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, which ranks it in the top 1.3% of all 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.
How do I remediate CVE-2021-21974?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21974, 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.

Dependency Blast Radius

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

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