[ CVE-2021-26855 · Published 3 Mar 2021 ]
Microsoft Exchange Server Remote Code Execution Vulnerability
Exploited · CISA KEV CVSS 9.1
EPSS 100%Fix available
[ Why it matters ]Priority signals
- Exploited in the wild: on CISA's Known Exploited Vulnerabilities list since 2021-11-03
- Known to be used in ransomware campaigns
- EPSS: 100% chance of exploitation in the next 30 days (higher than 100% of CVEs)
- Critical severity: CVSS 9.1
[ Description ]Official description
Microsoft Exchange Server Remote Code Execution Vulnerability
CISA: Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.
[ Fixes ]Fixes and patches
CISA required action (US federal deadline 3 May 2022): Apply updates per vendor instructions.
- Patch on msrc.microsoft.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD
- Patch on portal.msrc.microsoft.comVendor patch or bulletin · NVD · Reference tagged 'Patch' by NVD
[ References ]References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26855PatchVendor Advisory
- packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.…ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Executio…ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Down…ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.htmlExploitThird Party AdvisoryVDB Entry
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855PatchVendor Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalogUS Government Resource