CVE-2023-21529
Deserialization of Untrusted Data in Microsoft Exchange Server. CISA confirmed attackers exploit it and added it to its Known Exploited Vulnerabilities catalog on 13 April 2026.
- Product
- Microsoft Exchange Server
- Added to CISA's catalog
- Federal fix-by date
- Ransomware
- Known to be used in ransomware
- Vendor advisories
- Sources
- CISA’s catalog, NVD entry
CISA’s description.
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
More from Microsoft this year.
- CVE-2026-96951 Command Injection, added
- CVE-2026-65660 Code Injection, added
- CVE-2026-85880 Heap-Based Buffer Overflow, added
- CVE-2026-81963 Link Following, added
- CVE-2019-1068 Remote Code Execution, added
- CVE-2026-55040 Weak Authentication, added
- CVE-2026-33824 Double Free, added
- CVE-2026-68820 Use-After-Free, added
Every flaw CISA confirmed exploited in the last 30 days is on the exploit watch. This is not security advice. Check the vendor’s advisory before acting. From CISA’s catalog of 4 November 2026.