CVE-2021-31207

CRITICALNVD 6.69.0▲
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 6.6 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 3 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: 100%CVSS: 6.6Exploit: cisa kev · ssvc active · kev ransomware · Metasploit · epss top5pct · epss high · public exploitExposed: 0

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

Microsoft Exchange Server Security Feature Bypass Vulnerability

CVSS v3
6.6
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

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%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
100%
EPSS %ILE
100%
KEV
⚠ Exploited

Published

May 11, 2021

Last Modified

October 30, 2025

Advisory Details (4)

Auto-updated Jun 12, 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-2021-31207
generic

ZDI-21-819 - TrendAI™ Zero Day Initiative™ (ZDI)

https://www.zerodayinitiative.com/advisories/ZDI-21-819/
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-2021-31207
generic

Packet Storm

http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html

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 84× in last 7d / 355× 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 1,296 total refreshes for this CVE.

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

Publicly available exploits

(1 reference)

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

  • Metasploitexploit/windows/http/exchange_proxyshell_rce✓ verified
    First seen Apr 6, 2021

    Microsoft Exchange ProxyShell RCE

    Open source ↗

Related CVEs(same CWE)

Frequently asked(6)

What is CVE-2021-31207?
CVE-2021-31207 is a critical vulnerability published on May 11, 2021. Microsoft Exchange Server Security Feature Bypass Vulnerability
When was CVE-2021-31207 disclosed?
CVE-2021-31207 was first published in the National Vulnerability Database on May 11, 2021, with the most recent update on October 30, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-31207 actively exploited?
Yes. CISA added CVE-2021-31207 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-2021-31207?
CVE-2021-31207 has a CVSS v3 base score of 6.6 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2021-31207?
CVE-2021-31207 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-2021-31207?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-31207, 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-2021-31207

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