CVE-2021-27065VulnerabilityPublished 11/03/2021Updated 10/24/2026

CVE-2021-27065: Microsoft Exchange Server Remote Code Execution Vulnerability

Affects Microsoft Exchange ServerSource CISA KEV

Severity

High

No CVSS score published yet

Exploitation: Actively exploited – in CISA KEV since 11/03/2021
KEV deadline: 05/03/2022
Ransomware: Used in ransomware campaigns
EPSS: 99.9% chance of exploitation in 30 days – higher than 99% of CVEs

What to do

CISA required action

Apply updates per vendor instructions.

Description

CVE-2021-27065 is a remote code execution vulnerability in Microsoft Exchange Server. It is part of the ProxyLogon exploit chain and has been exploited in the wild. The vulnerability has been used in known ransomware campaigns. No specific affected versions or patch information is provided in the input data.

Summary

Microsoft Exchange Server contains an unspecified remote code execution vulnerability identified as CVE-2021-27065. This vulnerability is a component of the ProxyLogon exploit chain, which has been actively exploited in the wild. The exploit enables attackers to execute arbitrary code remotely on vulnerable Exchange Server instances. The vulnerability has been leveraged in ransomware campaigns, indicating its critical impact on affected systems. No detailed technical specifics or affected version ranges are provided in the input data.

Impact

The vulnerability allows remote attackers to execute arbitrary code on Microsoft Exchange Server systems, potentially leading to full system compromise. It has been exploited in the wild and is associated with ransomware campaigns, indicating significant operational and security impact for affected organizations.

Mitigation

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no patch or official fix information is provided in the input data, organizations should consult Microsoft’s official security advisories and apply recommended updates or mitigations promptly.

Weaknesses

CWE-39Unclassified weakness (opens in a new tab)

What to do

Description

AnalysisAI-generated, updated 10/24/2026, 09:10:59 UTC

Weaknesses

References

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