Is CVE-2021-26857 being actively exploited?

Yes. CVE-2021-26857 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added on November 3, 2021.

What is the CVSS score for CVE-2021-26857?

CVE-2021-26857 has a CVSS 3.1 base score of 7.8 (HIGH).

CVE-2021-26857

HIGH · CVSS 7.8CISA KEV: actively exploitedEPSS 95.8%EU EUVD: exploited

Microsoft Exchange Server Remote Code Execution Vulnerability

Key facts

CVSS score: 7.8 (v3.1)
Severity: HIGH
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-502
EPSS score: 95.8% (100th percentile)
In CISA KEV: Yes, added November 3, 2021
In EU EUVD: Yes (EUVD-2021-13641)
Published: March 3, 2021
NVD last modified: August 19, 2026
Status: Analyzed

CISA Known Exploited Vulnerability

Microsoft Exchange Server Remote Code Execution Vulnerability

Added to the KEV catalog on November 3, 2021; federal remediation due May 3, 2022. Known to be used in ransomware campaigns.

EU Vulnerability Database (EUVD)

This vulnerability is also tracked by ENISA as EUVD-2021-13641 in the EU Vulnerability Database. ENISA flags it as known exploited. Last updated in EUVD on August 19, 2026.

View on the EU Vulnerability Database

Affected products

microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server
microsoft / exchange server

Certified products that may be affected

1 FIPS 140 or Common Criteria certified product, from automated matching by sec-certs.org.

Microsoft Exchange Server 2010 SP1 Enterprise (English) 64-bit - Microsoft Corporation - Common Criteria Certificate Number: 2011/72 - archived

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26857(Patch, Vendor Advisory)
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26857(Patch, Vendor Advisory)
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26857(US Government Resource)

Last updated September 17, 2026 · Source: NVD, CISA KEV, FIRST.org EPSS

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