CVEs / CVE-2023-21529
CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
- Known exploited in the CISA KEV catalog since 13 Apr 2026
- high 8.8 CVSS 3.1 (from the CNA)
- EPSS 59.2% chance of exploitation in the next 30 days, higher than 99% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 | from 15.00.0, before 15.00.1497.047 | 15.00.1497.047 |
| Microsoft Microsoft Exchange Server 2016 Cumulative Update 23 | from 15.01.0, before 15.01.2507.021 | 15.01.2507.021 |
| Microsoft Microsoft Exchange Server 2019 Cumulative Update 11 | from 15.02.0, before 15.02.0986.041 | 15.02.0986.041 |
| Microsoft Microsoft Exchange Server 2019 Cumulative Update 12 | from 15.02.0, before 15.02.1118.025 | 15.02.1118.025 |
Exploitation
| In CISA KEV since | 13 Apr 2026 |
|---|---|
| Due date for US federal agencies | 27 Apr 2026 |
| Used in ransomware campaigns | Known |
| 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. |
Severity
| CVSS 3.1 | 8.8 highCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HScored by the CNA ([email protected]) |
|---|---|
| Weakness | CWE-502 |
References
- CVE-2023-21529 on NVD
- CVE-2023-21529 in the CISA KEV catalog
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 (cited by CISA)
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 Patch, Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-21529 US Government Resource
- https://www.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
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.