SharePoint Pre-Auth RCE chain (CVE-2023–29357 & CVE-2023–24955) | STAR Labs
Brief I may have achieved successful exploitation of a SharePoint target during Pwn2Own Vancouver 2023. While the live demonstration lasted only approximately 30 seconds, it is noteworthy that the process of discovering and crafting the exploit chain consumed nearly a year of meticulous effort and research to complete the full exploit chain. This exploit chain leverages two vulnerabilities to achieve pre-auth remote code execution (RCE) on the SharePoint server: Authentication Bypass – An unauthenticated attacker can impersonate as any SharePoint user by spoofing valid JSON Web Tokens (JWTs), using the none signing algorithm to subvert signature validation checks when verifying JWT tokens used for OAuth authentication.