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CVE-2023-21529

Microsoft Exchange Server Remote Code Execution Vulnerability

HIGH
8.8
CVSS Score
Published: February 14, 2023 at 07:33 PM UTC
Updated: August 19, 2026 at 05:35 PM UTC
1 product affected across 1 vendorExchange Server

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Severity
HIGH8.8
Exploitation
CISA KEV
Exploit prediction
EPSS 59%
SSVC
Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score59.3%

EPSS (Exploit Prediction Scoring System) estimates a 59.3% chance this CVE is exploited in the wild within the next 30 days — higher than 99% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.

Required Action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Ransomware Use
Known
Added to KEV
Apr 13, 2026
Remediation Due
Apr 27, 2026
187 days overdue
Notes
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529
https://nvd.nist.gov/vuln/detail/CVE-2023-21529

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 < 15.00.1497.04715.01.0 ≤ v < 15.01.2507.02115.02.0 ≤ v < 15.02.0986.04115.02.0 ≤ v < 15.02.1118.02515.00.015.01.015.02.02013 cumulative_update_232016 cumulative_update_232019 cumulative_update_112019 cumulative_update_12
Affected range stops below 15.00.1497.047, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2507.021, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0986.041, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.1118.025, 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 (3)

Vendor AdvisoryPatch
Source: [email protected]
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529
US Government Resource
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529
Technical Description
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
https://www.microsoft.com/en-us/security/blog/2026/04/06/storm-1175-focuses-gaze-on-vulnerable-web-facing-assets-in-high-tempo-medusa-ransomware-operations/

SSVC — Action Prioritization

SSVCActiveNot automatableTotal impact

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

CVSS

8.8HIGHmicrosoft
Vector?

Quick Info

StatusANALYZED
CWE
CWE-502NVD-CWE-noinfo

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