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01 Record

CVE-2021-26855

Microsoft Exchange Server Remote Code Execution Vulnerability

CriticalKEVPUBLISHEDCNA: microsoft
CNA base score9.1 CVSS v3.xCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C
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02 Description

Microsoft Exchange Server Remote Code Execution Vulnerability

03 Exploitation and scoring

Exploitation
Exploited in the wild. Listed in the CISA Known Exploited Vulnerabilities catalog on 2021-11-03. Federal remediation due 2022-05-03. Known ransomware campaign use: reported by CISA.
SSVC decision
  • ExploitationactiveCISA reports credible evidence of active exploitation.
  • AutomatableyesAn attacker can reliably automate reconnaissance through exploitation, so this scales.
  • Technical ImpacttotalSuccessful exploitation gives total control of the vulnerable component.
CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.
EPSS probability
99.99% probability of exploitation activity in the next 30 days.
EPSS percentile
Equal to or higher than the score of 99.9% of scored records. A rank, not a probability.
NVD base score
9.1 (CVSS v3.x), scored by the NVD independently of the CNA.
NVD CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD analysis status
Analyzed. NVD last modified this record on 2026-08-19.
Red Hat severity
No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

04 Metadata

Published
2021-03-02 23:55Z5 YR AGO
Last updated
2026-08-19 16:30Z2 MO AGO
Reserved
2021-02-08
Assigning CNA
microsoft
Record state
PUBLISHED
Severity
Critical (CVSS 9.1)
CNA CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C
Weaknesses
  • CWE-918Server-Side Request Forgery (SSRF)Base
Data version
5.2
Document digest
9f7b69ce4611419410671775081b07b706ca0dc14160e6387052e93d784f8a5d

05 Affected products

VendorProductVersionsPlatforms
MicrosoftMicrosoft Exchange Server 2013 Cumulative Update 2115.00.0 to < 15.00.1395.012x64-based Systems
MicrosoftMicrosoft Exchange Server 2013 Cumulative Update 2215.00.0 to < 15.00.1473.006x64-based Systems
MicrosoftMicrosoft Exchange Server 2013 Cumulative Update 2315.00.0 to < 15.00.1497.012x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1015.01.0 to < 15.01.1531.012x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1115.01.0 to < 15.01.1591.018x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1215.01.0 to < 15.01.1713.010x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1315.01.0 to < 15.01.1779.008x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1415.01.0 to < 15.01.1847.012x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1515.01.0 to < 15.01.1913.012x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1615.01.0 to < 15.01.1979.008x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1715.01.0 to < 15.01.2044.013x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1815.01.0 to < 15.01.2106.013x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 1915.01.0 to < 15.01.2176.009x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 815.01.0 to < 15.01.1415.010x64-based Systems
MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 915.01.0 to < 15.01.1466.016x64-based Systems
MicrosoftMicrosoft Exchange Server 201915.02.0 to < 15.02.0221.018x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 115.02.0 to < 15.01.1979.006x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 215.02.0 to < 15.02.0397.011x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 315.02.0 to < 15.02.0464.015x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 415.02.0 to < 15.02.0659.012x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 515.02.0 to < 15.02.0595.008x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 615.02.0 to < 15.02.0529.013x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 715.02.0 to < 15.02.0721.013x64-based Systems
MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 815.02.0 to < 15.02.0792.010x64-based Systems

06 References