CVE-2021-26857

CVE-2021-26857 is a high-severity (CVSS 7.8) vulnerability in Microsoft Exchange Server. CISA added it to the Known Exploited Vulnerabilities catalog on November 3, 2021, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by May 3, 2022. CISA also lists it as known to be used in ransomware campaigns, so it should be prioritised accordingly. Microsoft has 390 vulnerabilities in the KEV catalog, 117 of them linked to ransomware.

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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