Microsoft patches the three-flaw Copilot chain

Microsoft patched CoSnitch, a critical Copilot vulnerability chain that combined three flaws into a one-click route to prompt execution, connected-app data access, and persistent memory poisoning, according to Varonis’s disclosure. Varonis disclosed it in December 2025; patches shipped on August 18, 2026, and the researchers report no evidence of exploitation in the wild. The lesson for teams wiring agents into email and files is the same one behind Claude’s new write actions and approval trail: treat connectors and durable memory as a security boundary, not a convenience feature.