Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
- Vendor
- Microsoft
- Product
- Exchange Server
- CVSS
- 8.8
- EPSS (exploit probability)
- 59.3%
- Status
- kevransomware use
- CISA patch-by (BOD 22-01)
- Added to KEV
Is CVE-2023-21529 being exploited?
Yes. CISA added CVE-2023-21529 to its Known Exploited Vulnerabilities catalog on . CISA only lists a CVE when it has reliable evidence of exploitation in the wild. CISA marks it as known to be used in ransomware campaigns.
FIRST's EPSS model puts the probability of exploitation activity in the next 30 days at 59.3% (scored October 14, 2026).
- CISA KEV[ LISTED ]
- ENISA EUVD (exploited)[ — ]
- CIRCL KEV[ — ]
Catalog snapshot 2026-11-13. Full cross-catalog view: /kev-comparison
CVE-2023-21529 timeline
Every event links to its source. Catalog dates are each catalog's own; day offsets count from NVD publication. Data: JSON
What to do
CISA required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
US federal civilian agencies must remediate by (14 days after listing) under BOD 22-01. Everyone else: that deadline is a sensible upper bound, not a target. Vendor guidance and the NVD record are linked under Source above.
Other Microsoft Exchange Server CVEs we track
| CVE / Vulnerability | Severity | CVSS | EPSS | Added to KEV |
|---|---|---|---|---|
| CVE-2026-96940 Microsoft Exchange Server privilege escalation via weak authorizationwrite-up | [ HIGH ] | 8.8 | 2.7% | — |
| CVE-2021-31196 Microsoft Exchange Server Information Disclosure Vulnerability | [ HIGH ] | 7.2 | 54.1% | |
| CVE-2024-21410 Microsoft Exchange Server Privilege Escalation Vulnerability | [ CRITICAL ] | 9.8 | 12.7% | |
| CVE-2022-41080 Microsoft Exchange Server Privilege Escalation Vulnerabilityransomware use | [ HIGH ] | 8.8 | 77.3% | |
| CVE-2022-41082 Microsoft Exchange Server Remote Code Execution Vulnerabilityransomware use | [ HIGH ] | 8.0 | 100.0% | |
| CVE-2022-41040 Microsoft Exchange Server Server-Side Request Forgery Vulnerabilityransomware use | [ HIGH ] | 8.8 | 100.0% | |
| CVE-2018-8581 Microsoft Exchange Server Privilege Escalation Vulnerabilityransomware use | [ HIGH ] | 7.4 | 27.6% | |
| CVE-2021-33766 Microsoft Exchange Server Information Disclosure | [ HIGH ] | 7.3 | 98.2% |