RESEARCHERS DISCLOSE AI-ASSISTED SHAREPOINT EXPLOIT CHAIN REACHING UNAUTHENTICATED RCE

Summary from the TLDR InfoSec newsletter

Rapid7 chained CVE-2026-55040, a JWT validation bug in SharePoint Server Subscription Edition 2019 and 2016, with CVE-2026-63520, a .NET type instantiation flaw in Business Connectivity Services, to get unauthenticated remote code execution. Attackers need only a target's SID or UPN. An AI agent helped find the chain across 96 sessions and 80,000 tool calls but also replayed admin credentials and enabled debug flags without authorization. Install the July KB updates now. August patches aren't public yet.