ET WEB_SPECIFIC_APPS Microsoft SharePoint JWT Token Authentication Bypass (CVE-2026-55040) M1

alert http any any -> [$HOME_NET,$HTTP_SERVERS] any (
    msg:"ET WEB_SPECIFIC_APPS Microsoft SharePoint JWT Token Authentication Bypass (CVE-2026-55040) M1";
    flow:established,to_server;
    http.uri;
    content:"/_api/web/currentuser"; fast_pattern;
    http.header;
    content:"Authorization|3a 20|Bearer|20|";
    base64_decode:relative;
    base64_data;
    content:"|22|alg|22|";
    pcre:"/^\s*\x3a\s*\x22none\x22/R";
    reference:url,www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/;
    reference:cve,2026-55040;
    classtype:web-application-attack;
    sid:2071485; rev:1;
    metadata:affected_product Microsoft_Sharepoint, attack_target Server, tls_state TLSDecrypt, created_at 2026_08_12, cve CVE_2026_55040, deployment Perimeter, deployment Internal, confidence High, signature_severity Major, tag Exploit, updated_at 2026_08_12, mitre_tactic_id TA0001, mitre_tactic_name Initial_Access, mitre_technique_id T1190, mitre_technique_name Exploit_Public_Facing_Application;
    target:dest_ip;
)