ACTIVELY EXPLOITED
CVE-2021-26858: Microsoft Exchange Server Remote Code Execution Vulnerability
| Vendor | Microsoft |
|---|---|
| Product | Exchange Server |
| Actively exploited | Yes |
| Added to CISA KEV | 3 Nov 2021 |
| CISA federal deadline | 3 May 2022 |
| Ransomware use | Known |
Required action (CISA's text)
Apply updates per vendor instructions.
Description (NVD)
Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.
SOURCES
Other Microsoft flaws
- patchtuesday:2026-11: Vulnerability in Microsoft
- CVE-2026-124194: Microsoft Office Outlook Missing User Interaction for Potentially Unsafe Action Vulnerability
- CVE-2026-96951: Microsoft Windows Command Injection Vulnerability
- CVE-2026-65660: Microsoft SharePoint Code Injection Vulnerability
- CVE-2026-85880: Microsoft Windows Heap-Based Buffer Overflow Vulnerability
Data from NVD, CISA KEV, FIRST EPSS and vendor advisories. Updated 10 Nov 2026.