Prioritization
- NVD CVSS
- 9.8
- Published
- Mar 2, 2021 7:15 PM EST
- Modified
- Aug 19, 2026 3:22 PM EDT
- CISA KEV
- Yes
- KEV due date
- 2022-05-03
CISA required action
Apply updates per vendor instructions.
← Threat Center
9.8
CRITICAL • CVSS 3.1
CVE-2021-26855
CISA KNOWN EXPLOITEDMicrosoft Exchange Server Remote Code Execution Vulnerability
Red Hat context
No Red Hat-specific cached context is available for this record.
Recommended response
- Treat as priority because it appears in CISA Known Exploited Vulnerabilities data; follow the required action and due date where applicable.
- Identify affected assets with Qualys, Tanium, software inventory, CMDB or configuration-management data.
- Confirm package/application applicability before change execution; CVSS alone does not prove that every host is vulnerable.
- Patch, upgrade, rehydrate or apply a vendor-approved mitigation through controlled change. GraceITS can automate eligible waves with Ansible/Tanium.
- Rescan after remediation and reconcile remaining exceptions, false positives, unsupported systems and compensating controls.