CVE-2023-21529
KEVRansomware UseMicrosoft Exchange Server Deserialization of Untrusted Data Vulnerability
Description
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS 3.1 vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HPublishedFeb 14, 2023
Last modifiedAug 19, 2026
Added to KEVApr 13, 2026
Remediation dueApr 27, 2026
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529PatchVendor Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529US Government Resource
- microsoft.com/en-us/security/blog/2026/04/06/storm-1175-focuses-gaze-on-vulnerable-web-facing-assets-in-high-tempo-medusa-ransomware-operations/Technical Description
0 recent articles mention this CVE
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Risk assessment · Critical
Actively exploited and used by ransomware crews. Patch immediately.
- Exploitation
- Confirmed in the wild (CISA KEV)
- Federal remediation deadline
- Overdue by 182 days
- Ransomware
- Used in known ransomware campaigns
- CVSS
- 8.8 HIGH
- EPSS (30-day exploit probability)
- 59.3% · top 1% of all CVEs
- Weakness
- CWE-502
- Attack vector
- Network, remotely reachable
Recommended actions
- 1.Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- 2.Treat as emergency change: patch or isolate internet-facing instances first.
- 3.Review exposure: confirm which instances are reachable from the internet and restrict access until patched.
- 4.Hunt for compromise: review logs for the disclosure window, not just from the patch date.
- 5.Verify offline/immutable backups and segment the affected systems. This flaw is used for ransomware initial access.
Assessment is derived automatically from the live signals above; verify against your own asset inventory.