CVE-2021-26858: Microsoft Exchange Server Remote Code Execution Vulnerability

CVE-2021-26858 · Severity: critical · CVSS 7.8 · Exploited in the wild · Published 2021-11-03

Microsoft Exchange Server contains a remote code execution vulnerability that is part of the ProxyLogon exploit chain. The flaw allows an attacker to execute arbitrary code on the server, though CVSS metrics indicate a local attack vector with user interaction required.

Technologies: Microsoft Exchange Server. Vendors: Microsoft.

Quick answers

Is CVE-2021-26858 exploited in the wild?
Yes. CVE-2021-26858 is known to be exploited in the wild, first recorded on 3 November 2021. Treat it as urgent.
How severe is CVE-2021-26858?
Critical severity, with a CVSS score of 7.8, published 3 November 2021.
Which products and versions are affected?
Microsoft Exchange Server 2010 SP3, 2013 SP1, 2013 CU22, 2013 CU23, 2016 CU8-CU19, 2019 CU1-CU8.
Is there a fix for CVE-2021-26858?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2021-26858 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2021-26858?
Check whether you run Microsoft Exchange Server. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Affected products

  • Microsoft Exchange Server 2010 SP3, 2013 SP1, 2013 CU22, 2013 CU23, 2016 CU8-CU19, 2019 CU1-CU8

Timeline

  • 2021-03-02: disclosed: Initial disclosure of ProxyLogon vulnerabilities
  • 2021-03-08: other: Initial analysis by NIST
  • 2021-11-03: kev added: Added to CISA Known Exploited Vulnerabilities catalog

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