CVE-2021-31207

Name: CVE-2021-31207
Creator: NVD / NIST
Published: 2021-05-11T19:15:10.397+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.6/10Actively ExploitedEPSS 99.78%

Last modified Jun 17, 2026

CVE-2021-31207 is a medium-severity vulnerability rated 6.6/10 on the CVSS scale. Microsoft Exchange Server Security Feature Bypass Vulnerability. CISA has confirmed active exploitation in the wild. EPSS estimates a 99.78% chance of exploitation in the next 30 days.

Description

Microsoft Exchange Server Security Feature Bypass Vulnerability

Metrics

CVSS 3.1

6.6/10

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

99.78%

100.0th percentile

Probability of exploitation in the next 30 days. Learn more

Exploitation Status

This vulnerability is listed in CISA’s Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Federal agencies must remediate by Nov 17, 2021.

Weakness Enumeration

Affected Software

Vendor	Product	Versions	Update
Microsoft	Exchange Server	2013	Cumulative Update 23
Microsoft	Exchange Server	2016	Cumulative Update 19
Microsoft	Exchange Server	2019	Cumulative Update 8

References

http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207Patch, Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-819/Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207Patch, Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-819/Third Party Advisory, VDB Entry
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207US Government Resource

Timeline

Published: May 11, 2021
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2021-31207?

Microsoft Exchange Server Security Feature Bypass Vulnerability

How severe is CVE-2021-31207?

CVE-2021-31207 has a CVSS score of 6.6/10 (MEDIUM severity). The EPSS model estimates a 99.78% probability of exploitation in the next 30 days. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.

How do I fix CVE-2021-31207?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-31207?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST