CVE-2021-34523

CRITICALNVD 9.09.8▲
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 9.0 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
9.0
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS: 100%CVSS: 9.0Exploit: NoneExposed: 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
9.0
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
100.0%
KEV
⚠ Exploited

Published

July 14, 2021

Last Modified

October 30, 2025

Advisory Details (4)

Auto-updated Jun 1, 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 | Zero Day Initiative

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

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 / 347× 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 677 total refreshes for this CVE.

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

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 ↗

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 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-2021-34523 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 9.0 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.8.
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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