CVE-2021-26857CISA KEV

Microsoft Exchange Server Remote Code Execution Vulnerability

Severity unknownCVSS unknownCheck the vendor advisory for fixed versions

CISA lists this Microsoft vulnerability as known exploited. Its MSRC release detail is outside this installation's collected history.

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CISA catalog record

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

Product: Exchange Server
Added to KEV: 3 Nov 2021
Federal remediation due: 3 May 2022
Known ransomware use: Yes

Page history

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Field-level log (2)

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23 Oct 2026 · 09:33:49 UTC Source coverage: cisa-kevIncomplete → Current
23 Oct 2026 · 08:31:50 UTC Source coverage: cisa-kevCurrent → Incomplete

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Exploitation and risk

Source status

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CVE-2021-26857

Listed in CISA KEV · added 3 Nov 2021 · Microsoft · Exchange Server

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

CISA source

No EPSS score is available here for this CVE.

Saved 23 Oct 2026 16:01:26 UTC · View this risk record (JSON)

cve-program · CVE-2021-26857

Published

Microsoft Exchange Server Remote Code Execution Vulnerability

Source published: 2 Mar 2021 23:55:26 UTC
Source modified: 19 Aug 2026 16:30:15 UTC
Saved here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 7.8 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C