# CVE-2021-34473 (ProxyShell)

Microsoft Exchange Server Remote Code Execution Vulnerability

- Page: https://www.vulneraibility.com/cve/CVE-2021-34473
- CVSS: 9.1
- Known exploited: yes, in CISA KEV since 2021-11-03; CISA due date 2021-11-17; known ransomware use
- EPSS: 100.00% (percentile 100.0)
- Public exploit code: 1 Metasploit module · 9 GitHub proofs of concept · 1 Nuclei template (first 2021-08-10)
- CISA SSVC: exploitation active, automatable yes, technical impact total (assessed 2025-02-04)
- Weakness: CWE-918
- Published: 2021-07-14

## Affected versions

- Microsoft Microsoft Exchange Server 2013 Cumulative Update 23: affected >= 15.00.0 and < 15.00.1497.015
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 19: affected >= 15.01.0 and < 15.01.2176.012
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 20: affected >= 15.01.0 and < 15.01.2242.008
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 8: affected >= 15.02.0 and < 15.02.0792.013
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 9: affected >= 15.02.0 and < 15.02.0858.010

A version outside these ranges is not a statement that it is unaffected.

## References

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

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Summary, impact and action are written by the vulneraibility.com AI analysis pipeline from the CVE record, NVD, CISA and FIRST data; verify against the references.