CVE-2021-42321VulnerabilityPublished 11/17/2021Updated 10/24/2026

CVE-2021-42321: Microsoft Exchange Server Remote Code Execution Vulnerability

Affects Microsoft ExchangeSource CISA KEV

Severity

High

No CVSS score published yet

Exploitation: Actively exploited – in CISA KEV since 11/17/2021
KEV deadline: 12/01/2021
Ransomware: Used in ransomware campaigns
EPSS: 91.7% chance of exploitation in 30 days – higher than 99% of CVEs

What to do

CISA required action

Apply updates per vendor instructions.

nvd.nist.gov/vuln/detail/CVE-2021-42321 (opens in a new tab)

Description

CVE-2021-42321 is a high-severity remote code execution vulnerability in Microsoft Exchange Server. It arises from improper validation of cmdlet arguments, allowing an authenticated attacker to execute arbitrary code remotely. This vulnerability has been exploited in the wild and is known to have been used in ransomware campaigns.

Summary

CVE-2021-42321 affects Microsoft Exchange Server and involves improper validation of cmdlet arguments. An attacker with authentication privileges can leverage this flaw to perform remote code execution on the affected system. The vulnerability has been actively exploited in the wild, including use in ransomware attacks. No specific affected versions or patch information is provided in the available data.

Impact

Successful exploitation allows an authenticated attacker to execute arbitrary code remotely on Microsoft Exchange Server, potentially leading to full system compromise. The vulnerability has been exploited in real-world attacks and ransomware campaigns, indicating significant risk to affected organizations.

Mitigation

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since this is not a cloud service, organizations should monitor Microsoft advisories for official fixes or workarounds. Until a patch is applied, restrict access to Exchange management interfaces to trusted administrators only.

CVE-2021-42321: Microsoft Exchange Server Remote Code Execution Vulnerability

What to do

Description

Summary

Impact

Mitigation

Weaknesses

References

What to do

Description

AnalysisAI-generated, updated 10/24/2026, 09:42:27 UTC

Weaknesses

References

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