CVE-2021-26857

unknown KEV

Published 2021-11-03 · Modified 2021-11-03

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CVSS v3

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CVSS v4 NEW

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not yet in upstream

VIR risk

1.5

Description

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

CISA KEV

Vendor: Microsoft
Product: Exchange Server
Due date: 2022-05-03

Predictions

Exploit likelihood

99%

Patch ETA

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Heuristic predictions, AS-IS, for prioritization only.

Mitigations

vendor Authored 2026-05-27

{Vendor advisory: cisa-kev — 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-2021-26857}

Exploits

Public proof-of-concept code below. AS-IS, for defenders and authorised testing only.

References

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-2021-26857

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.