Secuno
ENNL
Book demo

CVE-2021-42321

Microsoft Exchange Server Remote Code Execution

8.8 HIGHActively exploited (CISA KEV)Used in ransomwarePublic exploitEPSS 91.7%
  1. Published10 Nov 2021
  2. Added to CISA KEV17 Nov 2021
  3. Remediation due1 Dec 2021
Actively exploited (CISA KEV)

An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.

Added to KEV: 17 Nov 2021Federal remediation due: 1 Dec 2021Used in ransomware

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

Microsoft Exchange Server2016 · 2019

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

Frequently asked

Is CVE-2021-42321 being actively exploited?

Yes. CVE-2021-42321 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 17 Nov 2021. It has been used in ransomware campaigns.

How severe is CVE-2021-42321?

CVE-2021-42321 has a CVSS 3.1 base score of 8.8, rated high. EPSS estimates a 91.7% probability of exploitation.

Which products are affected by CVE-2021-42321?

Affected products include Microsoft Exchange Server.

How do I fix CVE-2021-42321?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-42321 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

Running Microsoft 365?

Patching is one half. Scan your domain and check MFA, legacy authentication, admin roles and mail forwarding in two minutes, with a fix for every gap.

Run the free Microsoft 365 check

Get Patch this first every Monday

Five vulnerabilities that matter this week, ranked on real exploitation. Plain language, one email, no spam.

You can unsubscribe with one click from every issue. We handle your details as described in our privacy policy.

Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.