alert http any any -> $HOME_NET any (msg:"ET WEB_SPECIFIC_APPS n8n Ni8mare Content-Type Confusion Multipart Form Bypass (CVE-2026-21877) M1"; flow:established,to_server; http.request_body; content:"|22|executionId|22 3a|"; fast_pattern; content:"|22|files|22 3a|"; content:"|22|filepath|22 3a|"; pcre:"/^\s*\x22[^\x22]*?\x2f/R"; http.uri; content:"/form/"; startswith; http.content_type; content:"application/json"; http.method; content:"POST"; reference:url,www.cyera.com/research-labs/ni8mare-unauthenticated-remote-code-execution-in-n8n-cve-2026-21858; reference:cve,2026-21877; classtype:web-application-attack; sid:2066610; rev:1; metadata:attack_target Server, tls_state TLSDecrypt, created_at 2026_01_07, cve CVE_2026_21877, deployment Perimeter, deployment Internal, deployment SSLDecrypt, confidence High, signature_severity Major, tag Exploit, updated_at 2026_01_07, mitre_tactic_id TA0001, mitre_tactic_name Initial_Access, mitre_technique_id T1190, mitre_technique_name Exploit_Public_Facing_Application; target:dest_ip;)