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CVE record · CVE-2021-42321

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS 8.8 HighCriticalIn CISA KEV · ransomwareEPSS 0.92 · 99th percentile

Critical, because:

  • In CISA’s KEV catalogue since 17 Nov 2021: it is known to be exploited.
  • CVSS score 8.8 (7.0 or more) and EPSS 0.92 (0.1 or more): a high score and a real chance of exploitation in the next 30 days.

How we decide what’s critical

Published by the CVE Program (CNA: microsoft) at 10 Nov 2021, 00:47 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
VendorProductVersions
Microsoft Microsoft Exchange Server 2016 Cumulative Update 21
  • affected 15.01.0 to before 15.01.2308.020 custom
Microsoft Microsoft Exchange Server 2016 Cumulative Update 22
  • affected 15.0.0 to before 15.01.2375.017 custom
Microsoft Microsoft Exchange Server 2019 Cumulative Update 10
  • affected 15.02.0 to before 15.02.0792.019 custom
Microsoft Microsoft Exchange Server 2019 Cumulative Update 11
  • affected 15.02.0 to before 15.02.0986.014 custom
Identifiers
CVE-2021-42321
CNA
microsoft
Tags
Published
10 Nov 2021
Updated
19 Aug 2026

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

ScoreRatingCVSSVectorSource
8.8 High 3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C CNA (microsoft)
  • CISA KEV Listed since 17 Nov 2021: known to be exploited. CISA reports use in ransomware campaigns.
  • EPSS 0.92, the 99th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

This record came from the full history of the CVE Program, published 10 Nov 2021. New records show when each source confirmed them.

Sources

References from the CNA

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.