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CVE-2021-31206: Microsoft Exchange Server Remote Code Execution Vulnerability

• Severity: high (CVSS 7.9 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 13.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-07-14 · updated 2026-08-10

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Affected products

• Microsoft Exchange Server: 2013-cumulative_update_23, 2016-cumulative_update_20, 2016-cumulative_update_21, 2019-cumulative_update_10, 2019-cumulative_update_9
• Microsoft Exchange Server 2013 Cumulative Update 23: from 15.00.0 before 15.00.1497.023 — fixed in 15.00.1497.023
• Microsoft Exchange Server 2016 Cumulative Update 20: from 15.01.0 before 15.01.2242.012 — fixed in 15.01.2242.012
• Microsoft Exchange Server 2016 Cumulative Update 21: from 15.01.0 before 15.01.2308.014 — fixed in 15.01.2308.014
• Microsoft Exchange Server 2019 Cumulative Update 10: from 15.02.0 before 15.02.0922.013 — fixed in 15.02.0922.013
• Microsoft Exchange Server 2019 Cumulative Update 9: from 15.02.0 before 15.02.0858.015 — fixed in 15.02.0858.015

How to fix

Upgrade to a fixed version: Microsoft Exchange Server 2013 Cumulative Update 23 15.00.1497.023; Microsoft Exchange Server 2016 Cumulative Update 20 15.01.2242.012; Microsoft Exchange Server 2016 Cumulative Update 21 15.01.2308.014; Microsoft Exchange Server 2019 Cumulative Update 10 15.02.0922.013; Microsoft Exchange Server 2019 Cumulative Update 9 15.02.0858.015. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-31206
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31206
• https://www.zerodayinitiative.com/advisories/ZDI-21-826/

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