Name:Cisco Secure Firewall - Repeated Blocked Connections id:1f57f10e-1dc5-47ea-852c-2e85b2503d79 version:1 date:2025-04-02 author:Nasreddine Bencherchali, Splunk status:production type:Anomaly Description:The following analytic detects repeated blocked connection attempts from the same initiator to the same responder within a short time window. It leverages Cisco Secure Firewall Threat Defense logs and identifies connections where the action is set to Block, and the number of occurrences reaches or exceeds a threshold of ten within a one-minute span. This pattern may indicate a misconfigured application, unauthorized access attempts, or early stages of a brute-force or scanning operation. If confirmed malicious, this behavior may represent an attacker probing the network, attempting lateral movement, or testing firewall rules for weaknesses.
Data_source:
search:`cisco_secure_firewall` EventType=ConnectionEvent action=Block | bin _time span=1m | stats count min(_time) as firstTime max(_time) as lastTime Values(dest_port) as dest_port Values(url) as url by src_ip, dest, transport, rule, action | where count >= 10 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `cisco_secure_firewall___repeated_blocked_connections_filter`
how_to_implement:This search requires Cisco Secure Firewall Threat Defense Logs, which
includes the ConnectionEvent EventType. This search uses an input macro named `cisco_secure_firewall`.
We strongly recommend that you specify your environment-specific configurations
(index, source, sourcetype, etc.) for Cisco Secure Firewall Threat Defense logs. Replace the macro definition
with configurations for your Splunk environment. The search also uses a post-filter
macro designed to filter out known false positives.
The logs are to be ingested using the Splunk Add-on for Cisco Security Cloud (https://splunkbase.splunk.com/app/7404).
The access policy must also enable logging.
known_false_positives:Misconfigured applications or automated scripts may generate repeated blocked traffic, particularly if attempting to reach decommissioned or restricted resources.
Vulnerability scanners or penetration testing tools running in authorized environments may trigger this alert.
Tuning may be required to exclude known internal tools or scanner IPs from detection.
References: -https://www.cisco.com/c/en/us/td/docs/security/firepower/741/api/FQE/secure_firewall_estreamer_fqe_guide_740.pdf drilldown_searches: name:'View the detection results for - "$src_ip$"' search:'%original_detection_search% | search src_ip = "$src_ip$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$src_ip$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src_ip$") 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: - 'Cisco Secure Firewall Threat Defense Analytics' asset_type:Network security_domain:network mitre_attack_id: - 'T1018' - 'T1046' - 'T1110' - 'T1203' - 'T1595.002' product: - 'Splunk Enterprise' - 'Splunk Cloud' - 'Splunk Enterprise Security'
