CVEvulnerability

CVE-2021-26855

9.1 CRITICAL Known exploited Published 2021-03-03 Modified 2026-08-19 Official page ↗

CISA Known Exploited Vulnerability

Microsoft Exchange Server Remote Code Execution Vulnerability — Microsoft Exchange Server

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

Added to KEV
2021-11-03
Remediation due
2022-05-03
Ransomware use
Known
Required action
Apply updates per vendor instructions.
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
Status
Analyzed
Published
2021-03-03
Last modified
2026-08-19
Assigner
[email protected]
CVSS 3.1 ([email protected])
9.1 CRITICAL — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CVSS 3.1 ([email protected])
9.8 CRITICAL — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0 ([email protected])
7.5 HIGH — AV:N/AC:L/Au:N/C:P/I:P/A:P
Weaknesses
CWE-918

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Affected configurations

• microsoft exchange server 2013 • microsoft exchange server 2016 • microsoft exchange server 2019

Related

Weakness · CWE (1)

  • CWE-918 Server-Side Request Forgery weakness

Referenced by CWE · observed example (1)

  • CWE-918 Server-Side Request Forgery weakness

References