8.8

CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability

CVSS: 8.8v3.1HighKEVRansomwareAnalyzed
Published 14-02-2023Last modified 19-08-2026
Open JSON

Vulnerability summary

CVE-2023-21529 is a high (CVSS 8.8) Deserialization of Untrusted Data vulnerability in Microsoft Exchange Server. It is known to be exploited: CISA lists it, first on 13-04-2026. It has been used in ransomware campaigns. EPSS estimates a 59.29% chance of exploitation in the next 30 days, higher than 99.1% of scored vulnerabilities.

Overall risk
90/100
0100
Critical · default modelHow is this calculated?
CVSS score
8.8/10
010
High · v3.1 (CVE.org)
EPSS score
59.29%
0%100%
Critical · -2.81 pp in 30 days
KEVListedCISA
RansomwareKnown useFlagged by CISA
Public exploits0No public exploits recorded

Timeline

  1. 14-02-2023
    PublishedVulnerability first disclosed.
  2. 13-04-2026
    Added to CISA KEVMicrosoft Exchange Server Deserialization of Untrusted Data Vulnerability
  3. 27-04-2026
    CISA remediation dueApply mitigations per vendor instructions.
  4. 19-08-2026
    Last modifiedVulnerability information updated.

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS metrics

2 scores · 2 sources · 1 version

EPSS trend

Probability

59.29%

Chance of exploitation in the next 30 days

Percentile

99%

Versus all other CVEs

30-day change

-2.81 pp

From 62.10% on 20-09-2026

20-09-202620-10-2026
EPSS score
59.29%

Known exploited

Compare KEV catalogs
CISA KEVListed
Added
13-04-2026
Federal due date
27-04-2026
Ransomware

CISA 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. msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529 nvd.nist.gov/vuln/detail/CVE-2023-21529

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Microsoft5 products

1 vendor · 5 products

References

3 links