CVE-2021-31209

Name: CVE-2021-31209
Creator: NVD / NIST
Published: 2021-05-11T19:15:10.467+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 2.63%

Last modified Jun 17, 2026

CVE-2021-31209 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. Microsoft Exchange Server Spoofing Vulnerability. EPSS estimates a 2.63% chance of exploitation in the next 30 days.

Description

Microsoft Exchange Server Spoofing Vulnerability

Metrics

CVSS 3.1

6.5/10

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

EPSS Probability

2.63%

83.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-290

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

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31209Patch, Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-615/Third Party Advisory, VDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31209Patch, Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-615/Third Party Advisory, VDB Entry

Timeline

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

Frequently Asked Questions

What is CVE-2021-31209?

Microsoft Exchange Server Spoofing Vulnerability

How severe is CVE-2021-31209?

CVE-2021-31209 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 2.63% probability of exploitation in the next 30 days.

How do I fix CVE-2021-31209?

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-2021-31209?

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

Scan your code now

Source: NVD / NIST