CVE-2025-53690: 
Sitecore Experience Platform (XP) vulnerability analysis and mitigation

CVE-2025-53690 is a critical ViewState deserialization vulnerability affecting Sitecore Experience Manager (XM), Experience Platform (XP), Experience Commerce (XC), and Managed Cloud deployments. The vulnerability was discovered in September 2025 and is tracked with a CVSS score of 9.0 (Critical). The flaw affects any version of Sitecore XP 9.0 or earlier with Active Directory 1.4 or earlier that were deployed using sample machine keys provided in legacy deployment guides (NVD, Help Net Security).

The vulnerability stems from a ViewState deserialization flaw in ASP.NET configurations where sample machine keys were exposed in deployment guides. ViewStates are an ASP.NET feature that persists webpage states in hidden HTML fields named __VIEWSTATE. When machine keys protecting ViewState integrity are compromised, the application loses its ability to differentiate between legitimate and malicious ViewState payloads. The vulnerability specifically affects the /sitecore/blocked.aspx endpoint, which uses a hidden ViewState form accessible without authentication (Google Cloud Blog).

Successful exploitation of CVE-2025-53690 can lead to full remote code execution and unauthorized access to information. The vulnerability allows attackers to achieve initial system compromise, perform internal reconnaissance, establish persistence, and potentially move laterally within the network. Affected systems are at risk of data exfiltration, credential theft, and complete system compromise (Security Online, Help Net Security).

Sitecore has confirmed that its updated deployments automatically generate unique machine keys. Organizations should rotate and encrypt machine keys in all web.config files, restrict access to web.config to application administrators only, inspect environments for suspicious behavior, and adopt key rotation as a standard practice. Additionally, organizations should follow Microsoft's security best practices for ASP.NET, including implementing automated machine key rotation and enabling View State Message Authentication Code (MAC) (Google Cloud Blog, Security Online).

The vulnerability has garnered significant attention from the cybersecurity community, with Mandiant and Sitecore coordinating on the disclosure. CISA has added the vulnerability to its Known Exploited Vulnerabilities Catalog, requiring federal agencies to apply mitigations by September 25, 2025 (NVD).