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CVE-2021-34473

Microsoft Exchange Server Remote Code Execution Vulnerability

CRITICAL
9.1
CVSS Score
Published: July 14, 2021 at 05:54 PM UTC
Updated: August 10, 2026 at 08:18 PM UTC
1 product affected across 1 vendorExchange Server

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Severity
CRITICAL9.1
Exploitation
CISA KEV
Exploit prediction
EPSS 100%
SSVC
Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score100.0%

EPSS (Exploit Prediction Scoring System) estimates a 100.0% chance this CVE is exploited in the wild within the next 30 days — higher than 100% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution.

Required Action
Apply updates per vendor instructions.
Ransomware Use
Known
Added to KEV
Nov 3, 2021
Remediation Due
Nov 17, 2021
1810 days overdue
Notes
https://nvd.nist.gov/vuln/detail/CVE-2021-34473

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Exchange Server· Microsoft
95%
15.00.0 ≤ v < 15.00.1497.01515.01.0 ≤ v < 15.01.2176.01215.01.0 ≤ v < 15.01.2242.00815.02.0 ≤ v < 15.02.0792.01315.02.0 ≤ v < 15.02.0858.01015.00.015.01.015.02.02013 cumulative_update_232016 cumulative_update_192016 cumulative_update_202019 cumulative_update_82019 cumulative_update_9
Affected range stops below 15.00.1497.015, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2176.012, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2242.008, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0792.013, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0858.010, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (5)

ExploitThird Party AdvisoryVDB Entry
Source: [email protected]
http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
PatchVendor Advisory
Source: [email protected]
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473
Third Party AdvisoryVDB Entry
Source: [email protected]
https://www.zerodayinitiative.com/advisories/ZDI-21-821/
Vendor AdvisoryPatch
Source: cverecord
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34473
US Government Resource
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34473

SSVC — Action Prioritization

SSVCActiveAutomatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

9.1CRITICALmicrosoft
Vector?

Quick Info

StatusANALYZED
CWE
CWE-918

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