Warning: Zero-Day Vulnerability in Sitecore Products (CVE-2025-53690), Fix Immediately!

Critical zero-day CVE-2025-53690 affects Sitecore XM/XP/XC and related deployments that used publicly documented sample ASP.NET machine keys, allowing attackers to bypass ViewState protection and achieve remote code execution; Mandiant and other sources report active exploitation with privilege escalation, credential theft, persistence and custom malware delivery. Immediate actions recommended are applying vendor patches, rotating and protecting machineKey entries in web.config, restricting access, and increasing monitoring and incident response readiness because patching alone does not remediate prior compromise.