CVE-2021-26855
Microsoft Exchange Server Remote Code Execution Vulnerability
Actively exploited
- In the CISA exploited-vulnerabilities catalogue since Nov 3, 2021
- US federal agencies must remediate it by May 3, 2022 (BOD 22-01)
- Attacked 1 day before the vulnerability was made public
- Confirmed by sensors, not only by reports
- Used in ransomware campaigns
Apply updates per vendor instructions.
Source: CISA KEV · Oct 6, 2026 Oct 3, 2026 Oct 2, 2026 Oct 1, 2026 Sep 30, 2026 Sep 29, 2026
CVSS score9.1 / 10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NWeakness type (CWE)CWE-918, CWE-918
Vendorsmicrosoft
Affected products
| Vendors | Product | Versions |
|---|---|---|
| microsoft | exchange server | 2013 |
Related articles
NightEagle, Hacking Cat, and Toy Ghouls Target Russian Networks
Kaspersky reports NightEagle, Hacking Cat and Toy Ghouls targeting Russian firms with Exchange exploits, backdoors, ransomware and wipers.
FBI Disrupts QScan and QTRouter, the Chinese Network That Hid Attacks on US Infrastructure
FBI disrupts Chinese hacking platforms QScan and QTRouter used to attack US critical infrastructure, including NASA and Federal Reserve.
This product uses the NVD API but is not endorsed or certified by the NVD.