CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , 1,154 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 59.3%
EPSS score, percentile 99.1 of all scored records
- How severe?
- 8.8 High
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline . Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- Which versions are affected?
Affected
- from 15.00.0 to before 15.00.1497.047
- from 15.01.0 to before 15.01.2507.021
- from 15.02.0 to before 15.02.0986.041
- from 15.02.0 to before 15.02.1118.025
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
What to do
Required action, set by CISA
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA due date for this action: .
Advisories and patches
Linked from CISA's catalog entry
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529
- https://nvd.nist.gov/vuln/detail/CVE-2023-21529
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 15.00.0 to before 15.00.1497.047 |
| Status | Versions |
|---|---|
| Affected | from 15.01.0 to before 15.01.2507.021 |
| Status | Versions |
|---|---|
| Affected | from 15.02.0 to before 15.02.0986.041 |
| Status | Versions |
|---|---|
| Affected | from 15.02.0 to before 15.02.1118.025 |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
About this vulnerability
Microsoft Exchange Server contains a deserialization of untrusted data that allows an authenticated attacker to achieve remote code execution.
Summary: CISA's KEV catalog, as of .
- CISA added CVE-2023-21529 to its Known Exploited Vulnerabilities (KEV) catalog on 13 Apr 2026.
- CISA marks it as known to be used in ransomware campaigns.
- The due date CISA sets for the required action is 27 Apr 2026.
- The CVE record was published on 14 Feb 2023, 1,154 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 8.8 (High), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 59.3% (percentile 99.1), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Microsoft Exchange Server Remote Code Execution Vulnerability
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
Weakness
- CWE-502: Deserialization of Untrusted Data
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| Added to CISA KEV | |
| CISA due date for the required action | |
| CVE record last updated |
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