CVE-2021-28480

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
Elevated
9.8EG
EchelonGraph verdictMitigate this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 71%
CISA-KEV: Not listedEPSS PROB: 71%CVSS: 9.8Exploit: Elevated riskExposed services: Not assessed

A fix is referenced (a reference tagged "Patch", often a source commit), but no release containing it is confirmed — find the release that contains it; until it is applied, mitigate (WAF / firewall / segmentation).

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
77
EG Risk 77/100CISA 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
Severity98% × 45%
Exploitation71% × 40%
Automatability30% × 15%
CISA SSVC: Track at low, Track* at medium and Attend at high mission impact.
Action: A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it and apply that within your standard update timelines at low or medium mission impact and sooner than that at high; until then, restrict network exposure of the affected system or apply the vendor's mitigation.
EPSS PROB
71%
EPSS %ILE
99th
KEV
Not listed

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

A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it and apply that within your standard update timelines at low or medium mission impact and sooner than that at high; until then, restrict network exposure of the affected system or apply the vendor's mitigation.

Exploitation public PoC (EG-KEV: elevated) · Automatable unknown (not published for this CVE) · Technical impact total (CVSS ≥ 9.0). 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

April 13, 2021

Last Modified

November 21, 2024

Advisory Details (1)

Auto-updated Oct 4, 2026
Fix referenced — no release confirmed yet. Sources: microsoft.
microsoftMentions a patch (unverified)

Security Update Guide - Microsoft Security Response Center

Security Update Guide - Microsoft Security Response Center. Patch available via Microsoft Security Update

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-28480

Vendor Advisories for CVE-2021-28480(1)

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

Data Freshness Timeline

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

Publicly available exploits

(2 references)

Working exploit code is in the public domain (1 GitHub PoC). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCZephrFish/CVE-2021-28480_HoneyPoC3
    First seen Apr 21, 2021

    DO NOT RUN THIS.

    Open source ↗
  • Nucleihttp/cves/2021/CVE-2021-28480.yaml
    First seen Jan 1, 2021

    Microsoft Exchange - Pre-Auth SSRF / ACL Bypass (ProxyNotFound)

    Open source ↗

Frequently asked(5)

What is CVE-2021-28480?
CVE-2021-28480 is a critical vulnerability published on April 13, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability
When was CVE-2021-28480 disclosed?
CVE-2021-28480 was first published on April 13, 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-2021-28480 actively exploited?
CVE-2021-28480 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 71% probability of exploitation in the next 30 days (99th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-28480?
CVE-2021-28480 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-28480?
A fix for CVE-2021-28480 is referenced (a reference tagged "Patch", often a source commit), but EchelonGraph has no release containing it on record. Check that reference and the vendor's advisory for a release that contains the fix and update to it; until then, restrict network exposure of the affected system or apply the vendor's mitigation. The vendor advisories EchelonGraph has for CVE-2021-28480 are linked in the Vendor Advisories panel on this page.

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