CVE-2021-26857
Microsoft Exchange Server Remote Code Execution Vulnerability
- Published
- Mar 2, 2021
- Updated
- Aug 19, 2026
- Assigning CNA
- microsoft
- Evidence observed
- Nov 3, 2021
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HHigh · next 30 days
- Percentile
- 99.9%
- Model date
- Oct 19, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
CISA Known Exploited
This CVE appears in the CISA Known Exploited Vulnerabilities catalog.
Summary
Microsoft Exchange Server Remote Code Execution Vulnerability
Sources
- ProxyLogonExploit
Chaining CVE-2021-26855 and CVE-2021-26857 to exploit Microsoft Exchange
- exchange-0days-202103Detection
IoC determination for exploitation of CVE-2021-26855, CVE-2021-26857, CVE-2021-26858 and CVE-2021-27065.
- Proxylogon-exploitExploit
proxylogon exploit - CVE-2021-26857
- APT-BackpackExploit
cve-2019-11510, cve-2019-19781, cve-2020-5902, cve-2021-1497, cve-2021-20090, cve-2021-22006, cve-2021-22205, cve-2021-26084, cve-2021-26855, cve-2021-26857, cve-2021–26857, cve-2021–26858, cve-2021–26865
Responsible use
Use vulnerability information only on systems you own or are authorized to test. Kitploit links to public research metadata and does not store exploit code or malicious payloads.