ET HUNTING Sitecore Experience Platform ViewState Insecure Deserialization via Exposed ASP.NET MachineKeys (CVE-2025-53690)

alert http any any -> $HOME_NET any (
    msg:"ET HUNTING Sitecore Experience Platform ViewState Insecure Deserialization via Exposed ASP.NET MachineKeys (CVE-2025-53690)";
    flow:established,to_server;
    http.uri;
    content:"/sitecore/blocked.aspx"; fast_pattern;
    http.request_body;
    content:"__VIEWSTATE|3d|";
    pcre:"/^([a-zA-Z0-9]*%2[BF]){50,}/R";
    http.method;
    content:"POST";
    reference:url,cloud.google.com/blog/topics/threat-intelligence/viewstate-deserialization-zero-day-vulnerability;
    reference:cve,2025-53690;
    classtype:web-application-attack;
    sid:2064998; rev:1;
    metadata:affected_product Sitecore, attack_target Server, tls_state TLSDecrypt, created_at 2025_09_30, cve CVE_2025_53690, deployment Perimeter, deployment Internal, deployment SSLDecrypt, confidence High, signature_severity Major, tag Exploit, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2025_09_30, mitre_tactic_id TA0001, mitre_tactic_name Initial_Access, mitre_technique_id T1190, mitre_technique_name Exploit_Public_Facing_Application;
    target:dest_ip;
)