CVE-2021-26855—Microsoft Exchange Server Remote Code Execution Vulnerability

Vulnerability Name

Microsoft Exchange Server Remote Code Execution Vulnerability

Description

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.

Known To Be Used in Ransomware Campaigns?

Ransomware Status:

KNOWN

Action

Apply updates per vendor instructions.

Additional Notes

• Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26855

Related News Articles

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• Chinese Hacker Xu Zewei Arrested for Ties to Silk Typhoon Group and U.S. Cyber AttacksJuly 9, 2025
• Hackers Target Over 70 Microsoft Exchange Servers to Steal Credentials via KeyloggersJune 24, 2025
• US indicts Black Kingdom ransomware admin for Microsoft Exchange attacksMay 2, 2025

Related Weaknesses

• CWE-918