Microsoft Exchange Server Remote Code Execution Vulnerability. CVE-2021- 26857
Joint FBI-CISA Cybersecurity Advisory AA21-069A: Compromise of Microsoft Exchange Server - On March 2, 2021, Microsoft released out-of-band security updates to address vulnerabilities affecting Microsoft Exchange Server products.
- On March 3, 2021, after CISA and partners observed active exploitation of vulnerabilities, CISA issued Emergency Directive 21-02: Mitigate Microsoft Exchange On-Premises Product Vulnerabilities and Alert AA21-062A: Mitigate Microsoft Exchange Server Vulnerabilities.
- On March 31, 2021, CISA issued ED 21-02 Supplemental Direction V1, which directs federal departments and agencies to run newly developed tools—Microsoft’s Test-ProxyLogon.ps1 scriptand Safety Scanner MSERTto investigate whether their Microsoft Exchange Servers have been compromised.
- On April 13, 2021, CISA issued ED 21-02 Supplemental Direction V2, which directs federal departments and agencies to apply Microsoft's April 2021 Security Updatethat newly discloses and mitigates significant vulnerabilities affecting on-premises Exchange Server 2013, 2016, and 2019.