SANS Stormcast Wednesday, December 17th, 2025: Beyond RC4; Forticloud SSO Vuln Exploited; FortiGate SSO Exploited;

Beyond RC4 for Windows authentication Microsoft outlined its transition plan to move away from RC4 for authentication and published guidance and tools to facilitate this change. https://www.microsoft.com/en-us/windows-server/blog/2025/12/03/beyond-rc4-for-windows-authentication FortiCloud SSO Login Vuln Exploited Arctic Wolf observed exploit attempts against vulnerable FortiGate appliances. https://arcticwolf.com/resources/blog/arctic-wolf-observes-malicious-sso-logins-following-disclosure-cve-2025-59718-cve-2025-59719/ FrePBX Vulnerability Horizon3.ai identified three distinct vulnerabilities in FreePBX. In particular, the authentication by-pass issue should be of concern, but default FreePBX installs do not use the vulnerable web authentication feature. https://horizon3.ai/attack-research/the-freepbx-rabbit-hole-cve-2025-66039-and-others/