CVE-2021-1730: 
vulnerability analysis and mitigation

A spoofing vulnerability (CVE-2021-1730) exists in Microsoft Exchange Server that could allow a malicious actor to impersonate users. The vulnerability was disclosed in February 2021 and affects Microsoft Exchange Server installations (NVD, CVE Mitre).

The vulnerability is related to how Microsoft Exchange Server handles cross-site requests and cookies. It specifically involves the SameSite cookies standard implementation, which is designed to protect against cross-site request forgery (CSRF) attacks. The vulnerability received a CVSS v3.1 Base Score of 5.4 (Medium) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N, indicating network accessibility with low attack complexity but requiring user interaction (NVD).

If exploited, this vulnerability could allow attackers to perform spoofing attacks and impersonate legitimate users within the Exchange Server environment. The impact primarily affects the confidentiality and integrity of the system, with no direct impact on availability (NVD).

The vulnerability requires network access and user interaction for successful exploitation. The attack complexity is considered low, and no authentication is required to execute the attack (NVD).

Microsoft recommends implementing the Download Domains feature as a mitigation strategy. This involves creating a new DNS CNAME record pointing to the Outlook Web Access (OWA) domain, updating SSL certificates to include the new subdomain, and configuring Exchange Server settings using specific PowerShell commands. The feature causes attachments to be loaded from a different URL than the one used for OWA access, enforcing the SameSite cookies standard for better protection against CSRF attacks (Microsoft Learn).