CISA KEV catalog
Confirmed active exploitation.
Listed in CISA's catalog of Known Exploited Vulnerabilities: attackers are using it in real attacks. Patch it with priority.
- Name
- Microsoft Exchange Server Remote Code Execution Vulnerability
- Added to catalog
- Remediation due date (US federal)
- Required action
- Apply updates per vendor instructions.
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Affected products
microsoft: exchange server
References7
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26855 PatchVendor Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-… PatchVendor Advisory
- packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SS… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLo… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Un… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLo… ExploitThird Party AdvisoryVDB Entry
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=… US Government Resource
Metrics
- CVSS 3.1
-
9.1
CRITICAL
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N - EPSS — exploit probability
- 100% percentile: 100 · as of 2 November 2026
- CWE
- CWE-918
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.