Name:HTTP Duplicated Header id:1606cc5b-fd5f-4865-9fe3-0ed1eaec2df6 version:1 date:2025-10-15 author:Raven Tait, Splunk status:production type:Anomaly Description:Detects when a request has more than one of the same header. This is commonly used in request smuggling and other web based attacks. HTTP Request Smuggling exploits inconsistencies in how front-end and back-end servers parse HTTP requests by using ambiguous or malformed headers to hide malicious requests within legitimate ones. Attackers leverage duplicate headers, particularly Content-Length and Transfer-Encoding, to cause different servers in the chain to disagree on where one request ends and another begins. RFC7230 states that a sender MUST NOT generate multiple header fields with the same field name in a message unless either the entire field value for that header field is defined as a comma-separated list or the header field is a well-known exception. Data_source:
-Suricata
search:`suricata` http.request_headers{}.name="*" | rename dest_ip as dest | spath path=http.request_headers{}.name output=header_names | mvexpand header_names | where lower(header_names) != "set-cookie" | stats count by _raw, header_names, src_ip, dest | where count > 1 | stats values(header_names) as duplicate_headers by _raw, count, src_ip, dest | `http_duplicated_header_filter`
how_to_implement:This detection requires the Web datamodel to be populated from a supported Technology Add-On like Suricata, Splunk for Apache, Splunk for Nginx, or Splunk for Palo Alto. Some of these will need to have all headers dumped to contain the necessary fields. known_false_positives:False positives are not expected, however, monitor, filter, and tune as needed based on organization log sources. References: -https://portswigger.net/web-security/request-smuggling#what-is-http-request-smuggling -https://portswigger.net/research/http1-must-die -https://www.vaadata.com/blog/what-is-http-request-smuggling-exploitations-and-security-best-practices/ -https://www.securityweek.com/new-http-request-smuggling-attacks-impacted-cdns-major-orgs-millions-of-websites/ drilldown_searches: name:'View the detection results for - "$dest$"' search:'%original_detection_search% | search dest = "$dest$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$dest$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") starthoursago=168 | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' tags: analytic_story: - 'HTTP Request Smuggling' asset_type:Network mitre_attack_id: - 'T1071.001' - 'T1190' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' security_domain:network
