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

criticalknown exploitedpublic exploitCVE-2021-42321
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.

CSIRTS triage

vendor: Microsoftproduct: Exchange ServerRemote code execution
What
The vulnerability allows an authenticated attacker to perform remote code execution due to improper validation.
Who is affected
Authenticated users of Microsoft Exchange Server are affected.
Urgency
Remediation is critical as the vulnerability is actively exploited.
Action
Apply the latest security patches for Microsoft Exchange Server.

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Details

Source
CISA Known Exploited Vulnerabilities (US · database · site)
Severity
critical
Published
2021-11-17
Exploitation
Observed in the wild (CISA KEV)

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-42321

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2021-42321coverage & exploitation statusNVD · CVE.org

Recent advisories for Microsoft Exchange Server

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

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