CVE-2021-34473

CRITICALNVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score elevated to 9.8 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 9.8 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
9.8EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 100%CVSS: 9.8Exploit: 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 Remote Code Execution Vulnerability

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
99(Act)
EG Risk 99/100SSVC: 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
Severity98% × 45%
Exploitation100% × 40%
Automatability100% × 15%
Action: Fix now — active exploitation, automatable, high impact.
EPSS PROB
100%
EPSS %ILE
100%
KEV
⚠ Exploited

Published

July 14, 2021

Last Modified

August 10, 2026

Advisory Details (5)

Auto-updated Sep 14, 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-2021-34473
generic

ZDI-21-821 - TrendAI™ Zero Day Initiative™ (ZDI)

https://www.zerodayinitiative.com/advisories/ZDI-21-821/
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-2021-34473
generic

Packet Storm Security

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

Security Update Guide - Microsoft Security Response Center

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

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34473

Vendor Advisories for CVE-2021-34473(1)

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

Weakness Classification(1)

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 88× in last 7d / 362× 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 1,332 total refreshes for this CVE.

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

Publicly available exploits

(10 references)

Working exploit code is in the public domain (2 Metasploit modules) (7 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCipsBruno/CVE-2021-34473-NMAP-SCANNER
    First seen Nov 16, 2022

    A massive scanner for CVE-2021-34473 Microsoft Exchange Windows Vulnerability

    Open source ↗
  • GitHub PoCkh4sh3i/ProxyShell
    First seen Jun 29, 2022

    CVE-2021-34473 Microsoft Exchange Server Remote Code Execution Vulnerability

    Open source ↗
  • GitHub PoCje6k/CVE-2021-34473-Exchange-ProxyShell
    First seen Nov 22, 2021

    对Exchange Proxyshell 做了二次修改，精确的拆分、实现辅助性安全测试。

    Open source ↗
  • GitHub PoChorizon3ai/proxyshell
    First seen Sep 4, 2021

    Proof of Concept for CVE-2021-34473, CVE-2021-34523, and CVE-2021-31207

    Open source ↗
  • GitHub PoCp2-98/CVE-2021-34473
    First seen Aug 16, 2021

    CVE-2021-34473 Microsoft Exchange Server Remote Code Execution Vulnerability

    Open source ↗
  • GitHub PoCRaouzRouik/CVE-2021-34473-scanner
    First seen Aug 11, 2021

    Scanner for CVE-2021-34473, ProxyShell, A Microsoft Exchange On-premise Vulnerability

    Open source ↗
  • GitHub PoCcyberheartmi9/Proxyshell-Scanner
    First seen Aug 10, 2021

    nuclei scanner for proxyshell ( CVE-2021-34473 )

    Open source ↗
  • Metasploitexploit/windows/http/exchange_proxyshell_rce✓ verified
    First seen Aug 9, 2021

    Exchange ProxyShell chain — combined with CVE-2021-34523 and CVE-2021-31207 for RCE.

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

    Microsoft Exchange ProxyShell RCE

    Open source ↗
  • Nucleihttp/cves/2021/CVE-2021-34473.yaml
    First seen Jan 1, 2021

    Exchange Server - Remote Code Execution

    Open source ↗

Frequently asked(6)

What is CVE-2021-34473?
CVE-2021-34473 is a critical vulnerability published on July 14, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability
When was CVE-2021-34473 disclosed?
CVE-2021-34473 was first published in the National Vulnerability Database on July 14, 2021, with the most recent update on August 10, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-34473 actively exploited?
Yes. CISA added CVE-2021-34473 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-2021-34473?
CVE-2021-34473 has a CVSS v3 base score of 9.8 (NVD).
Which products are affected by CVE-2021-34473?
CVE-2021-34473 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-2021-34473?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-34473, 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-2021-34473

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