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CVE-2023-21529

Microsoft Exchange Server Deserialization of Untrusted Data

8.8 HIGHActively exploited (CISA KEV)Used in ransomwareEPSS 59.3%
  1. Published14 Feb 2023
  2. Added to CISA KEV13 Apr 2026
  3. Remediation due27 Apr 2026
Actively exploited (CISA KEV)

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

Added to KEV: 13 Apr 2026Federal remediation due: 27 Apr 2026Used in ransomware

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

Microsoft Exchange Server2013 · 2016 · 2019

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

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Frequently asked

Is CVE-2023-21529 being actively exploited?

Yes. CVE-2023-21529 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 13 Apr 2026. It has been used in ransomware campaigns.

How severe is CVE-2023-21529?

CVE-2023-21529 has a CVSS 3.1 base score of 8.8, rated high. EPSS estimates a 59.3% probability of exploitation.

Which products are affected by CVE-2023-21529?

Affected products include Microsoft Exchange Server.

How do I fix CVE-2023-21529?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2023-21529 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.