Microsoft Exchange Server Remote Code Execution Vulnerability

HIGH 7.8EXPLOITED (CISA KEV)CVE-2021-26858 · Published 03/03/2021 · updated 01/10/2026

Microsoft Exchange Server Remote Code Execution Vulnerability. Actively exploited: CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 03/11/2021. Patch affected systems as an emergency. It is known to be used in ransomware campaigns.

In short

CVE-2021-26858 is a HIGH (CVSS 7.8) vulnerability affecting exchange server (microsoft).
Exploited in the wild: CISA added it to the KEV catalog on 03/11/2021.
Chance of exploitation in the next 30 days (EPSS): 93.7%, higher than 99.8% of all vulnerabilities.
No patched version is listed yet: follow the vendor's advisory in References.

Package	Affected versions	Patched versions
exchange server microsoft	`= 2013= 2016= 2019`	No fix yet

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858 · Patch
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858 · Patch
cisa.gov/known-exploited-vulnerabilities-catalog · US Government Resource
CISA KEV · CVE-2021-26858

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In short

CVE-2021-26858 is a HIGH (CVSS 7.8) vulnerability affecting exchange server (microsoft).

Exploited in the wild: CISA added it to the KEV catalog on 03/11/2021.

Chance of exploitation in the next 30 days (EPSS): 93.7%, higher than 99.8% of all vulnerabilities.

No patched version is listed yet: follow the vendor's advisory in References.

Package

Affected versions

Patched versions

exchange server

microsoft

= 2013= 2016= 2019

No fix yet

More vulnerabilities in exchange server

See all →