Microsoft Exchange Server's Deserialization of Untrusted Data Enables Authenticated Attackers to Achieve Remote Code Execution; CISA's April 27th KEV Deadline Has Passed

Last refreshed2026-09-27

Status: KEV | Advisory ID: CVE-2023-21529

Key Details

CVE	CVE-2023-21529
Vulnerability Name	Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
Affected products	Microsoft Exchange Server
Exploitation status	Listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating confirmed active exploitation.
Classified as	CWE-502 (Deserialization of Untrusted Data)
KEV listing	Added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2026-04-13.
Exploitation prediction (EPSS)	59.29% probability of exploitation in the next 30 days (99% percentile) -- FIRST.org's EPSS model.
Federal remediation deadline	2026-04-27 (CISA KEV, Binding Operational Directive).

Affected Products, Subsystems & Sectors

Vendor	Product	Affected Versions	Patch Status
Microsoft	Exchange Server

Vendor

Product

Affected Versions

Patch Status

Microsoft

Exchange Server

Subsystems	General OT
Sectors	Multiple

What to Know

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

What to Do

Monitor Microsoft's web page for any future patch releases.

References

Source	Reference
NVD	https://nvd.nist.gov/vuln/detail/CVE-2023-21529
CVE	https://www.cve.org/CVERecord?id=CVE-2023-21529

Source

Reference

NVD

https://nvd.nist.gov/vuln/detail/CVE-2023-21529

CVE

https://www.cve.org/CVERecord?id=CVE-2023-21529

KEV Required Action

Field	Value
KEV Link	https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Date Added to KEV	2026-04-13
Required Action Due Date	2026-04-27
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.

Field

Value

KEV Link

https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Date Added to KEV

2026-04-13

Required Action Due Date

2026-04-27

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.