Exploited vulnerability · CISA KEV

Is CVE-2023-21529 exploited? Yes: in CISA KEV since 13 Apr 2026

Gociux · Microsoft Exchange Server · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2023-21529, Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 13 Apr 2026, 1154 days after it was published. It is known to be used in ransomware campaigns. It affects Microsoft Exchange Server. If you run it, CISA's required action is: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

What it is

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

What to do

1. Check whether you run it. Look for Exchange Server in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
2. Apply the fix. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 14 Feb 2023.
4. Get told next time. Email alerts when CISA adds a CVE for Microsoft.

Other exploited CVEs in Exchange Server

• CVE-2021-31196: Microsoft Exchange Server Information Disclosure Vulnerability (21 Aug 2024)
• CVE-2024-21410: Microsoft Exchange Server Privilege Escalation Vulnerability (15 Feb 2024)
• CVE-2022-41080: Microsoft Exchange Server Privilege Escalation Vulnerability (10 Jan 2023)
• CVE-2022-41082: Microsoft Exchange Server Remote Code Execution Vulnerability (30 Sep 2022)
• CVE-2022-41040: Microsoft Exchange Server Server-Side Request Forgery Vulnerability (30 Sep 2022)
• CVE-2018-8581: Microsoft Exchange Server Privilege Escalation Vulnerability (3 Mar 2022)

References

• msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529
• nvd.nist.gov/vuln/detail/CVE-2023-21529

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in April 2026 · Microsoft scorecard · act-now radar.