Name:Cisco Secure Firewall - Potential Data Exfiltration id:3d8536b6-52b4-4c3e-b695-3f2e90bb22be version:1 date:2025-04-02 author:Nasreddine Bencherchali, Splunk status:production type:Anomaly Description:The following analytic detects potentially suspicious large outbound data transfers from internal to external networks. It leverages Cisco Secure Firewall Threat Defense logs and calculates the total volume of data exchanged per connection by summing InitiatorBytes and ResponderBytes. Connections exceeding 100 MB are flagged, as these may indicate unauthorized data exfiltration, especially if initiated by unusual users, hosts, or processes. This analytic is scoped to inside-to-outside flows using a macro (cisco_secure_firewall_inside_to_outside) to abstract environment-specific zone definitions. If confirmed malicious, this behavior may reflect data staging and exfiltration over an encrypted or stealthy transport.
Data_source:
search:`cisco_secure_firewall` EventType=ConnectionEvent `cisco_secure_firewall_inside_to_outside` | eval total_bytes = InitiatorBytes + ResponderBytes | eval total_mb = round(total_bytes / 1024 / 1024, 2) | where total_mb >= 100 | eval Exfiltrated = total_mb + " MB" | stats min(_time) as firstTime max(_time) as lastTime Values(url) as url Values(rule) as rule Values(dest_port) as dest_port by src_ip, dest, Exfiltrated, transport, action | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `cisco_secure_firewall___potential_data_exfiltration_filter`
how_to_implement:This search requires Cisco Secure Firewall Threat Defense Logs, which
includes the ConnectionEvent EventType. This search uses two input macros named `cisco_secure_firewall` and `cisco_secure_firewall_inside_to_outside`.
We strongly recommend that you specify your environment-specific configurations
(index, source, sourcetype, etc.) for Cisco Secure Firewall Threat Defense logs. Replace the macro definitions
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:Large outbound transfers may occur due to legitimate activities such as cloud backups, file syncing, OS or application updates, or developer build deployments.
Backup servers, CI/CD pipelines, and enterprise sync tools (e.g., OneDrive, Dropbox) may exhibit similar patterns.
Additional validation using user context, scheduled task windows, or endpoint telemetry is recommended to reduce false positives.
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: - 'T1041' - 'T1567.002' - 'T1048.003' product: - 'Splunk Enterprise' - 'Splunk Cloud' - 'Splunk Enterprise Security'
