Overview
Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.
Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26857
Key Details
| Property | Value |
|---|---|
| CVE ID | CVE-2021-26857 |
| Vendor / Product | Microsoft — Exchange Server |
| NVD Published | 2021-03-03 |
| NVD Last Modified | 2025-12-18 |
| CVSS 3.1 Score | 7.8 |
| CVSS 3.1 Vector | CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
| Severity | HIGH |
| CWE | CWE-502 |
| CISA KEV Added | 2021-11-03 |
| CISA KEV Deadline | 2022-05-03 |
| Known Ransomware Use | ⚠️ Yes |
CVSS 3.1 Breakdown
Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Required Action
CISA BOD 22-01 Deadline: 2022-05-03.
Apply updates per vendor instructions.
Timeline
| Date | Event |
|---|---|
| 2021-11-03 | Added to CISA Known Exploited Vulnerabilities catalog |
| 2022-05-03 | CISA BOD 22-01 remediation deadline |
References
| Resource | Type |
|---|---|
| NVD — CVE-2021-26857 | Vulnerability Database |
| CISA KEV Catalog Entry | US Government |