CVE-2021-34473 — Microsoft Exchange Server Security Risk

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Known exploited / historically exploited security risk

CVE-2021-34473 — Microsoft Exchange Server

A Microsoft Exchange Server remote code execution vulnerability associated with active exploitation campaigns and included in CISA's Known Exploited Vulnerabilities program.

Business relevance

If Microsoft Exchange Server is present in your environment, confirm whether the installed version and configuration are affected. The existence of this CVE does not by itself prove that a specific system is vulnerable or compromised.

What to check

• Identify on-premises Microsoft Exchange servers.
• Record Exchange version and cumulative update level.
• Confirm applicable Microsoft security updates are installed.
• Review internet exposure and compromise indicators where applicable.

Source record

Authoritative source: CISA advisories on exploited Microsoft Exchange vulnerabilities and Known Exploited Vulnerabilities program.

CompFlorida record reviewed: September 21, 2026.

Vendor: Microsoft
Product: Microsoft Exchange Server
CVE: CVE-2021-34473