CVE-2021-26427

Name: CVE-2021-26427
Creator: NVD / NIST
Published: 2021-10-13T01:15:09.213+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9/10EPSS 0.87%

Last modified Jun 17, 2026

CVE-2021-26427 is a critical-severity vulnerability rated 9/10 on the CVSS scale. Microsoft Exchange Server Remote Code Execution Vulnerability. EPSS estimates a 0.87% chance of exploitation in the next 30 days.

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Metrics

CVSS 3.1

9/10

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

EPSS Probability

0.87%

54.2th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions	Update
Microsoft	Exchange Server	2013	Cumulative Update 23
Microsoft	Exchange Server	2016	Cumulative Update 21
Microsoft	Exchange Server	2019	Cumulative Update 10

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26427Patch, Vendor Advisory
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26427Patch, Vendor Advisory

Timeline

Published: Oct 13, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-26427?

Microsoft Exchange Server Remote Code Execution Vulnerability

How severe is CVE-2021-26427?

CVE-2021-26427 has a CVSS score of 9/10 (CRITICAL severity). The EPSS model estimates a 0.87% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26427?

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-2021-26427?

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

Scan your code now

Source: NVD / NIST