CVE-2021-26858

CRITICALNVD 7.89.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 7.8 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 5 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 94%CVSS: 7.8Exploit: cisa kev · ssvc active · kev ransomware · epss top5pct · epss highExposed: 0

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

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3
7.8
EG Score
9.0(high)
EG Risk
96(Act)
EG Risk 96/100SSVC: Act

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
Severity90% × 45%
Exploitation100% × 40%
Automatability100% × 15%
Action: Fix now — active exploitation, automatable, high impact.
EPSS PROB
94%
EPSS %ILE
100%
KEV
⚠ Exploited

Published

March 3, 2021

Last Modified

August 19, 2026

Advisory Details (2)

Auto-updated Jun 4, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: microsoft, cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858
microsoft Patch Available

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-2021-26858

Vendor Advisories for CVE-2021-26858(1)

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

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 94× in last 7d / 330× 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 984 total refreshes for this CVE.

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

Frequently asked(6)

What is CVE-2021-26858?
CVE-2021-26858 is a critical vulnerability published on March 3, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability
When was CVE-2021-26858 disclosed?
CVE-2021-26858 was first published in the National Vulnerability Database on March 3, 2021, with the most recent update on August 19, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-26858 actively exploited?
Yes. CISA added CVE-2021-26858 to the Known Exploited Vulnerabilities catalog on November 3, 2021, affecting Microsoft Exchange Server. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-26858?
CVE-2021-26858 has a CVSS v3 base score of 7.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2021-26858?
CVE-2021-26858 affects Microsoft Exchange Server. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2021-26858?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-26858, 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

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