Exploited vulnerabilities / CVE-2023-21529
Confirmed exploited · remote code execution · Microsoft Exchange ServerCVE-2023-21529
Microsoft Exchange Server remote code execution, confirmed exploited in the wild.
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
| CISA's name for it | Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability |
|---|---|
| Vendor and product | Microsoft · Exchange Server |
| Type | remote code execution · CWE-502 |
| Exploited | Confirmed by CISA listed 13 April 2026 |
| Likelihood | one of the most likely to be exploited of every vulnerability tracked |
| Deadline | 27 April 2026 · already passed |
| Used in ransomware | Yes: CISA reports it used in ransomware campaigns |
| Advisories | msrc.microsoft.com ↗ · nvd.nist.gov ↗ |
Three steps, in this order
Patch to the fixed version the vendor names, today if the product faces the internet.
Until it is patched, take the affected service off the internet or put it behind a VPN or allow-list.
Look for signs it was already used: new accounts, web shells, unexpected processes and outbound connections since the date it was listed.
| CISA's 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. |
|---|
Know before someone else finds it
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CVE-2023-21529 in short
Is CVE-2023-21529 being exploited?
Yes. CISA added CVE-2023-21529 to its Known Exploited Vulnerabilities catalogue on 13 April 2026, which it does only on evidence of exploitation in the wild.
What is the CISA deadline for CVE-2023-21529?
US federal agencies must remediate it by 27 April 2026. Everyone else should treat that date as the latest safe point to patch an internet-facing system.
How likely is CVE-2023-21529 to be exploited in the next 30 days?
FIRST's Exploit Prediction Scoring System gives it 59%, the 99th percentile of every CVE it scores.
How do I fix CVE-2023-21529?
Patch to the fixed version the vendor names, today if the product faces the internet. Until it is patched, take the affected service off the internet or put it behind a VPN or allow-list. Look for signs it was already used: new accounts, web shells, unexpected processes and outbound connections since the date it was listed.
Other Microsoft vulnerabilities being exploited
| CVE | Product | Type | Listed |
|---|---|---|---|
| CVE-2026-124194 | Office | exploited vulnerability | 10 November 2026 |
| CVE-2026-96951 | Windows | command injection | 13 October 2026 |
| CVE-2026-65660 | SharePoint | exploited vulnerability | 25 September 2026 |
| CVE-2026-81963 | Windows | privilege escalation | 8 September 2026 |
| CVE-2026-85880 | Windows | privilege escalation | 8 September 2026 |
| CVE-2019-1068 | SQL Server | remote code execution | 26 August 2026 |
Sources: CISA Known Exploited Vulnerabilities catalogue (released 10 November 2026) and FIRST EPSS. Page compiled automatically by SAK T.L.M, the threat-intelligence tool of SAK T.E.C, on 13 November 2026.