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 — 5 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: 9.0Exploit: 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
9.0
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 PROB
100%
EPSS %ILE
100%
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 56× in last 7d / 346× 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 727 total refreshes for this CVE.

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