Detection: Cisco Secure Firewall - Rare Snort Rule Triggered

Description

This analytic identifies Snort signatures that have triggered only once in the past 7 days across all Cisco Secure Firewall IntrusionEvent logs. While these rules typically do not trigger in day-to-day network activity, their sudden appearance may indicate early-stage compromise, previously unseen malware, or reconnaissance activity against less commonly exposed services. Investigating these outliers can provide valuable insight into new or low-noise adversary behaviors.

 1`cisco_secure_firewall` EventType=IntrusionEvent earliest=-7d
 2
 3| stats dc(_time) as TriggerCount min(_time) as firstTime max(_time) as lastTime 
 4        values(signature) as signature 
 5        values(src_ip) as src_ip 
 6        values(dest) as dest 
 7        values(dest_port) as dest_port
 8        values(transport) as transport
 9        values(app) as app 
10        values(rule) as rule 
11        by signature_id class_desc MitreAttackGroups InlineResult InlineResultReason
12
13| where TriggerCount = 1
14
15| `security_content_ctime(firstTime)`
16
17| `security_content_ctime(lastTime)`
18
19| `cisco_secure_firewall___rare_snort_rule_triggered_filter`

Data Source

Name Platform Sourcetype Source
Cisco Secure Firewall Threat Defense Intrusion Event N/A 'cisco:sfw:estreamer' 'not_applicable'

Macros Used

Name Value
cisco_secure_firewall sourcetype="cisco:sfw:estreamer"
cisco_secure_firewall___rare_snort_rule_triggered_filter search *
cisco_secure_firewall___rare_snort_rule_triggered_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1598 Phishing for Information Reconnaissance
T1583.006 Web Services Resource Development
Reconnaissance
Weaponization
DE.AE
CIS 13

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event False
This configuration file applies to all detections of type hunting.

Implementation

This search requires Cisco Secure Firewall Threat Defense Logs, which includes the IntrusionEvent 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 intrusion access policy must also be configured.

Known False Positives

False positives may occur with certain rare activity. Apply additional filters where required.

Associated Analytic Story

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation Passing N/A N/A N/A
Unit Passing Dataset not_applicable cisco:sfw:estreamer
Integration ✅ Passing Dataset not_applicable cisco:sfw:estreamer

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range


Source: GitHub | Version: 1