CVE-2020-1025: 
vulnerability analysis and mitigation

CVE-2020-1025 is an elevation of privilege vulnerability discovered in Microsoft SharePoint Server and Skype for Business Server. The vulnerability was disclosed on July 14, 2020, and stems from improper handling of OAuth token validation. This security flaw affects multiple versions of Microsoft products including SharePoint Enterprise Server 2016, SharePoint Foundation 2013 SP1, SharePoint Server 2019, and various versions of Skype for Business (NVD).

The vulnerability received a CVSS v3.1 base score of 9.8 (CRITICAL) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. The technical root cause is related to improper input validation (CWE-20) in the OAuth token validation process. The vulnerability allows an attacker to bypass authentication by modifying the OAuth token, potentially leading to unauthorized access to the affected systems (NVD, Rapid7).

If successfully exploited, this vulnerability allows an attacker to bypass authentication mechanisms and achieve improper access to the affected systems. The critical CVSS score of 9.8 indicates that the vulnerability can lead to a complete compromise of system confidentiality, integrity, and availability (NVD).

To exploit this vulnerability, an attacker would need to modify the OAuth token. The vulnerability can be exploited remotely without requiring user interaction or special privileges (NVD).

Microsoft addressed this vulnerability by modifying how SharePoint Server and Skype for Business Server validate tokens. The fix was released as part of the July 2020 security updates. For Skype for Business Server 2019 CU 2, users must install the July 2020 cumulative update 7.0.2046.236 for Core Components, Web Components Server, and Macp Web Components (Microsoft Support).