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 — 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: 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 53× in last 7d / 327× 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 669 total refreshes for this CVE.

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

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 vendor + 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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