CVE-2021-34473

As of 2025-10-29, CVE-2021-34473 is a CVSS 9.1 (CRITICAL-severity) vulnerability. CISA KEV-listed (known exploited). EPSS exploitation probability 94.2%. Threadlinqs Intelligence tracks 3 threats exploiting it.

Last updated: 2025-10-29

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3 vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Weaknesses (CWE)

CWE-918

Exploitation status

CISA KEV-listed (known exploited)

Threats tracking this CVE

• BlackCat/ALPHV Ransomware Abuses Azure Storage Account Keys via Sphynx Encryptor to Mass-Encrypt Cloud Storage — HIGH
• FamousSparrow APT Targets Azerbaijani Oil & Gas Industry via Exchange ProxyShell/ProxyNotShell (Deed RAT, Terndoor, Mofu Loader) — CRITICAL
• UAT-8099 (China) BadIIS Malware Campaign Targeting IIS Servers for SEO Fraud — HIGH

References

• http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473
• https://www.zerodayinitiative.com/advisories/ZDI-21-821/
• http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473
• https://www.zerodayinitiative.com/advisories/ZDI-21-821/
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34473

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Enriched from CVE.org, NVD (this product uses the NVD API but is not endorsed or certified by the NVD), FIRST EPSS, CISA KEV, and GitHub Security Advisories.