Critical severity · published Mar 2, 2021
CVE-2021-26855
Microsoft Exchange Server Remote Code Execution Vulnerability
RansomwareIn wildKEV
9.1
CVSS
100%
EPSS
Yes
On KEV
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)100.0% · higher than 100% of CVEs
Exploited in the wildYes
CISA KEVListed Nov 3, 2021
Federal remediation dueMay 3, 2022
Ransomware campaign useKnown
Affected products
Which versions
ES
Exchange Server · Microsoft
2013; 2013; 2013; 2016; 2016; 2016; +18 more · source: NVD, KEV
ME
Microsoft Exchange Server 2013 Cumulative Update 21 · Microsoft
15.00.0 before 15.00.1395.012 · source: vendor
ME
Microsoft Exchange Server 2013 Cumulative Update 22 · Microsoft
15.00.0 before 15.00.1473.006 · source: vendor
ME
Microsoft Exchange Server 2013 Cumulative Update 23 · Microsoft
15.00.0 before 15.00.1497.012 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 10 · Microsoft
15.01.0 before 15.01.1531.012 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 11 · Microsoft
15.01.0 before 15.01.1591.018 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 12 · Microsoft
15.01.0 before 15.01.1713.010 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 13 · Microsoft
15.01.0 before 15.01.1779.008 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 14 · Microsoft
15.01.0 before 15.01.1847.012 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 15 · Microsoft
15.01.0 before 15.01.1913.012 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 16 · Microsoft
15.01.0 before 15.01.1979.008 · source: vendor
ME
Microsoft Exchange Server 2016 Cumulative Update 17 · Microsoft
15.01.0 before 15.01.2044.013 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-26855
CVE.org
https://www.cve.org/CVERecord?id=CVE-2021-26855
CISA KEV catalogue
https://www.cisa.gov/known-exploited-vulnerabilities-catalog
vendor-advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26855
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