All vulnerabilities
CVE-2021-31207

Microsoft Exchange Server Security Feature Bypass Vulnerability

Microsoft Exchange ServerApplications & CMS
Open in ThreatlineRecord JSON
CVSS
6.6Medium
ExploitationExploited in the wildAdded to KEV 3 Nov 2021. Known ransomware useCISA KEV
Exploit odds (EPSS)99.8%Chance of exploitation activity in the next 30 days, higher than 99.9% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in15.00.1497.018Also 15.02.0858.012, 15.01.2242.010 and 2 moreCVE List
Federal deadline17 Nov 2021Remediation due date for US federal agenciesCISA KEV
CISA required actionApply updates per vendor instructions. CISA KEV

What fixes it

  • 15.00.1497.018Microsoft Exchange Server 2013 Cumulative Update 23CVE List
  • 15.02.0858.012Microsoft Exchange Server 2019 Cumulative Update 9CVE List
  • 15.01.2242.010Microsoft Exchange Server 2016 Cumulative Update 20CVE List
  • 15.01.2176.014Microsoft Exchange Server 2016 Cumulative Update 19CVE List
  • 15.02.0792.015Microsoft Exchange Server 2019 Cumulative Update 8CVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Timeline

  1. 6 Apr 2021Exploit code publicMetasploit
  2. 11 May 2021, 19:11 UTCPublishedCVE List
  3. 3 Nov 2021Added to CISA KEVCISA KEV

Public exploit code and templates 1

  • Exploit moduleMicrosoft Exchange ProxyShell RCE 6 Apr 2021Metasploit

Listed so defenders can prioritize. Threatline links to the source and does not host exploit code.

Description

Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass.

Text from CVE List

Affected versions 5

  • Microsoft Exchange Server 2013 Cumulative Update 23affected: 15.00.0 before 15.00.1497.018CVE List
  • Microsoft Exchange Server 2019 Cumulative Update 9affected: 15.02.0 before 15.02.0858.012CVE List
  • Microsoft Exchange Server 2016 Cumulative Update 20affected: 15.01.0 before 15.01.2242.010CVE List
  • Microsoft Exchange Server 2016 Cumulative Update 19affected: 15.01.0 before 15.01.2176.014CVE List
  • Microsoft Exchange Server 2019 Cumulative Update 8affected: 15.02.0 before 15.02.0792.015CVE List

References 4