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CVE record · CVE-2021-31207

Microsoft Exchange Server Security Feature Bypass Vulnerability

CVSS 6.6 MediumCriticalIn CISA KEV · ransomwareEPSS 1.00 · 99th percentile

Critical, because:

  • In CISA’s KEV catalogue since 3 Nov 2021: it is known to be exploited.

How we decide what’s critical

Published by the CVE Program (CNA: microsoft) at 11 May 2021, 19:11 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 2013 Cumulative Update 23
  • affected 15.00.0 to before 15.00.1497.018 custom
Microsoft Microsoft Exchange Server 2019 Cumulative Update 9
  • affected 15.02.0 to before 15.02.0858.012 custom
Microsoft Microsoft Exchange Server 2016 Cumulative Update 20
  • affected 15.01.0 to before 15.01.2242.010 custom
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19
  • affected 15.01.0 to before 15.01.2176.014 custom
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8
  • affected 15.02.0 to before 15.02.0792.015 custom
Identifiers
CVE-2021-31207
CNA
microsoft
Weakness (CWE)
CWE-434
Tags
Published
11 May 2021
Updated
21 Oct 2025

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
6.6 Medium 3.1 CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C CNA (microsoft)
  • CISA KEV Listed since 3 Nov 2021: known to be exploited. CISA reports use in ransomware campaigns.
  • EPSS 1.00, 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 11 May 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.