CVE-2021-34473: 
vulnerability analysis and mitigation

CVE-2021-34473 is a critical Remote Code Execution (RCE) vulnerability in Microsoft Exchange Server, specifically affecting the Autodiscover service. The vulnerability was discovered and disclosed in July 2021, and it is part of the ProxyShell vulnerability chain. This security flaw received a CVSS score of 10.0, indicating maximum severity (ZDI Advisory).

The vulnerability exists within the Autodiscover service of Microsoft Exchange Server and stems from improper validation of URI prior to accessing resources. The technical nature of this flaw allows remote attackers to execute arbitrary code on affected installations of Microsoft Exchange Server without requiring authentication. When combined with other vulnerabilities, attackers can leverage this to execute arbitrary code in the context of SYSTEM privileges (ZDI Advisory).

The exploitation of this vulnerability can lead to complete system compromise, allowing attackers to execute arbitrary code on vulnerable machines. The critical CVSS score of 10.0 (AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H) indicates that the vulnerability can result in complete loss of confidentiality, integrity, and availability of the affected system (Rapid7).

Microsoft released security updates in May 2021 to address this vulnerability. CISA strongly urges organizations to identify vulnerable systems on their networks and immediately apply Microsoft's Security Update, which remediates all three ProxyShell vulnerabilities (CISA Alert).