CVE-2021-26857

HIGHNVD 7.89.0▲
EchelonGraph scoreMEDIUM 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 — 4 sources updated this weekExploited in the wild
7.8
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS: 94%CVSS: 7.8Exploit: NoneExposed: 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(medium)
EPSS
99.8%
KEV
⚠ Exploited

Published

March 3, 2021

Last Modified

December 18, 2025

Advisory Details (2)

Auto-updated Jun 3, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: cisa, microsoft.
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-2021-26857
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-2021-26857

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 120× in last 7d / 506× 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 736 total refreshes for this CVE.

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

Publicly available exploits

(1 reference)

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 PoCsirpedrotavares/Proxylogon-exploit
    First seen Mar 11, 2021

    proxylogon exploit - CVE-2021-26857

    Open source ↗

Related CVEs(same vendor + same CWE)

Frequently asked(6)

What is CVE-2021-26857?
CVE-2021-26857 is a high vulnerability published on March 3, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability
When was CVE-2021-26857 disclosed?
CVE-2021-26857 was first published in the National Vulnerability Database on March 3, 2021, with the most recent update on December 18, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-26857 actively exploited?
Yes. CISA added CVE-2021-26857 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-2021-26857?
CVE-2021-26857 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-2021-26857?
CVE-2021-26857 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-2021-26857?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-26857, 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-2021-26857

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