CVE-2021-34523

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 Elevation of Privilege Vulnerability

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
84(Attend)
EG Risk 84/100SSVC: 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
Severity98% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
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-2021-34523
generic

ZDI-21-822 - TrendAI™ Zero Day Initiative™ (ZDI)

https://www.zerodayinitiative.com/advisories/ZDI-21-822/
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-2021-34523
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-2021-34523

Vendor Advisories for CVE-2021-34523(1)

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

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 91× in last 7d / 383× 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 1,399 total refreshes for this CVE.

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

Publicly available exploits

(3 references)

Working exploit code is in the public domain (1 Metasploit module) (2 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCSUPRAAA-1337/CVE-2021-34523
    First seen Sep 2, 2023

    test-yaml

    Open source ↗
  • GitHub PoCmithridates1313/ProxyShell_POC
    First seen Oct 2, 2021

    POC for scanning ProxyShell(CVE-2021-34523,CVE-2021-34473,CVE-2021-31207)

    Open source ↗
  • 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-2021-34523?
CVE-2021-34523 is a critical vulnerability published on July 14, 2021. Microsoft Exchange Server Elevation of Privilege Vulnerability
When was CVE-2021-34523 disclosed?
CVE-2021-34523 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-2021-34523 actively exploited?
Yes. CISA added CVE-2021-34523 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-2021-34523?
CVE-2021-34523 has a CVSS v3 base score of 9.8 (NVD).
Which products are affected by CVE-2021-34523?
CVE-2021-34523 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-2021-34523?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-34523, 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-2021-34523

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