CVE-2021-26855
Microsoft Exchange Server Remote Code Execution Vulnerability
IN CISA KEV
Microsoft Exchange Server Remote Code Execution Vulnerability
- Vendor
- Microsoft
- Product
- Exchange Server
- CVSS 3.1
- 9.1 (critical), scored by secure@microsoft.comCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CVSS 3.1
- 9.8 (critical), scored by NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CWE
- CWE-918
- Published
- 2021-03-03
- NVD modified
- 2026-08-19
- NVD status
- Analyzed
CISA KEV
- Date added
- 2021-11-03
- Due date
- 2022-05-03
- Ransomware use
- Known
- Required action
- Apply updates per vendor instructions.
EPSS
100% chance of exploitation in the next 30 days (percentile 99th)
FIRST EPSS, updated 17 Oct 2026. About EPSS
CVSS is severity, EPSS is likelihood, KEV means already exploited. EPSS is a statistical probability, not a certainty: a low score does not make a bug safe, and a high one does not prove it is being exploited.
References
- msrc.microsoft.com (Patch, Vendor Advisory)
- portal.msrc.microsoft.com (Patch, Vendor Advisory)
- www.cisa.gov (US Government Resource)
Data last updated 18 Oct 2026. Sources: NVD API 2.0, CISA KEV catalog, FIRST EPSS. Links: NVD, CISA KEV. Metadata only. ThreatWire does not host exploit code.