CVE DATABASE / CVE-2021-26857
CVE-2021-26857
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS 7.8 · HIGH
⚠ CISA KEV — ACTIVELY EXPLOITED
RANSOMWARE
On the CISA KEV catalog
Confirmed exploited in the wild. Added 2021-11-03.
Federal remediation due 2022-05-03.
Required action: Apply updates per vendor instructions.
Summary
Microsoft Exchange Server Remote Code Execution Vulnerability
CVSS 3.1 breakdown
| Base score | 7.8 (HIGH) |
| Vector | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
| Attack vector | LOCAL |
| Attack complexity | LOW |
| Privileges required | NONE |
| User interaction | REQUIRED |
| Scope | UNCHANGED |
| Confidentiality | HIGH |
| Integrity | HIGH |
| Availability | HIGH |
Weakness type (CWE)
Affected products
Microsoft exchange server
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References
- 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
Data: NIST NVD + CISA KEV. NVD last modified 2025-12-18. Always verify against the vendor advisory before acting.