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Vulnerabilities

Vulnerability · CVE-2021-31207

Microsoft Exchange Server Security Feature Bypass Vulnerability

Published May 11, 2021 · catalog updated Jun 16, 2026 · Microsoft Exchange Server

Patch now

CVE-2021-31207 is in the CISA known-exploited catalog, due Nov 17, 2021. Confirm Microsoft Exchange Server against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
Severity
Medium6.6
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
99.78%
Remediation
Remediation guidance
Affected products
cpe microsoft/exchange server · vendor Microsoft Exchange Server

Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass. Initial-access exploit intelligence.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe microsoft/exchange server2013
  • cpe microsoft/exchange server2016
  • cpe microsoft/exchange server2019
  • vendor Microsoft Exchange Serverversion unspecified

How to fix CVE-2021-31207

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2021-31207 is in the CISA known-exploited catalog, due Nov 17, 2021. Confirm Microsoft Exchange Server against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with microsoft/exchange server 2013; microsoft/exchange server 2016; microsoft/exchange server 2019. Apply updates per vendor instructions.

What should an analyst verify?

CWE-20: Improper Input Validation; CWE-434: Unrestricted Upload of File with Dangerous Type. EPSS 99.78%. The CISA KEV listing is the exploitation evidence. A public exploit reference is linked in Sources. That is not the same as confirmed exploitation. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. May 11, 2021 · Catalog

    Detected

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

  2. Nov 3, 2021 · CISA KEV

    Known exploited

    Apply updates per vendor instructions.

  3. Nov 17, 2021 · CISA KEV

    Remediation due

    Apply updates per vendor instructions.

  4. Jun 16, 2026 · Catalog

    Updated

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

Sources

  • CISA KEVConfirmed exploitationCVE-2021-31207

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

    cisa.gov
  • CVE.orgVulnerability recordCVE-2021-31207

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-31207

    30-day exploitation probability 99.8%

    first.org
  • Metasploit ModulesPublic exploit moduleexploit_windows/http/exchange_proxyshell_rce

    Public module reference (excellent). Module source is not copied into this catalog.

    rapid7.com
  • NIST NVDVulnerability recordCVE-2021-31207

    Microsoft Exchange Server Security Feature Bypass Vulnerability

    nvd.nist.gov
  • Packet Storm SecurityCited referencehttp://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html

    Packet Storm link already published on the finding.

    packetstormsecurity.com
  • VulnCheck KEVConfirmed exploitationCVE-2021-31207

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

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.