# CVE-2021-26857

Microsoft Exchange Server Remote Code Execution Vulnerability

- Page: https://www.vulneraibility.com/cve/CVE-2021-26857
- CVSS: 7.8
- Known exploited: yes, in CISA KEV since 2021-11-03; CISA due date 2022-05-03; known ransomware use
- EPSS: 95.76% (percentile 99.9)
- Unvetted proof-of-concept code on GitHub: 1 GitHub proof of concept (first 2021-03-11)
- CISA SSVC: exploitation active, automatable no, technical impact total (assessed 2021-03-02)
- Weakness: CWE-502
- Published: 2021-03-03

## Affected versions

- Microsoft Microsoft Exchange Server 2010 Service Pack 3: affected >= 14.0.0.0 and < 14.03.0513.000
- Microsoft Microsoft Exchange Server 2013 Cumulative Update 21: affected >= 15.00.0 and < 15.00.1395.012
- Microsoft Microsoft Exchange Server 2013 Cumulative Update 22: affected >= 15.00.0 and < 15.00.1473.006
- Microsoft Microsoft Exchange Server 2013 Cumulative Update 23: affected >= 15.00.0 and < 15.00.1497.012
- Microsoft Microsoft Exchange Server 2013 Service Pack 1: affected >= 15.00.0 and < 15.00.0847.064
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 10: affected >= 15.01.0 and < 15.01.1531.012
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 11: affected >= 15.01.0 and < 15.01.1591.018
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 12: affected >= 15.01.0 and < 15.01.1713.010
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 13: affected >= 15.01.0 and < 15.01.1779.008
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 14: affected >= 15.01.0 and < 15.01.1847.012
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 15: affected >= 15.01.0 and < 15.01.1913.012
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 16: affected >= 15.01.0 and < 15.01.1979.008
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 17: affected >= 15.01.0 and < 15.01.2044.013
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 18: affected >= 15.01.0 and < 15.01.2106.013
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 19: affected >= 15.01.0 and < 15.01.2176.009
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 8: affected >= 15.01.0 and < 15.01.1415.010
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 9: affected >= 15.01.0 and < 15.01.1466.016
- Microsoft Microsoft Exchange Server 2019: affected >= 15.02.0 and < 15.02.0221.018
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 1: affected >= 15.02.0 and < 15.01.1979.006
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 2: affected >= 15.02.0 and < 15.02.0397.011
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 3: affected >= 15.02.0 and < 15.02.0464.015
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 4: affected >= 15.02.0 and < 15.02.0659.012
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 5: affected >= 15.02.0 and < 15.02.0595.008
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 6: affected >= 15.02.0 and < 15.02.0529.013
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 7: affected >= 15.02.0 and < 15.02.0721.013
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 8: affected >= 15.02.0 and < 15.02.0792.010

A version outside these ranges is not a statement that it is unaffected.

## References

- [patch] https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26857
- [other] https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26857
- [other] https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26857

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Summary, impact and action are written by the vulneraibility.com AI analysis pipeline from the CVE record, NVD, CISA and FIRST data; verify against the references.