Detection: Cisco Secure Firewall - Blocked Connection

Updated Date: 2025-05-02 ID: 17e9b764-3a2b-4d36-9751-32d13ce4718b Author: Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects a blocked connection event by identifying a "Block" value in the action field. It leverages logs from Cisco Secure Firewall Threat Defense devices. This activity is significant as it can identify attempts from users or applications initiating network connection to explicitly or implicitly blocked range or zones. If confirmed malicious, attackers could be attempting to perform a forbidden action on the network such as data exfiltration, lateral movement, or network disruption.

1`cisco_secure_firewall` EventType=ConnectionEvent action=Block
2
3| stats count min(_time) as firstTime max(_time) as lastTime by src_ip, dest, dest_port, transport, rule, url, EVE_Process, action
4
5| `security_content_ctime(firstTime)` 
6
7| `security_content_ctime(lastTime)` 
8
9| `cisco_secure_firewall___blocked_connection_filter`

Data Source

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

Macros Used

Name Value
cisco_secure_firewall sourcetype="cisco:sfw:estreamer"
cisco_secure_firewall___blocked_connection_filter search *
cisco_secure_firewall___blocked_connection_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
T1018 Remote System Discovery Discovery
T1046 Network Service Discovery Discovery
T1110 Brute Force Credential Access
T1203 Exploitation for Client Execution Execution
T1595.002 Vulnerability Scanning Reconnaissance
Exploitation
Installation
Reconnaissance
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 True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

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

Blocked connection events are generated via an Access Control policy on the Firewall management console. Hence no false positives should be present.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A connection request from $src_ip$ to $dest$ has been blocked according to the configured firewall rule $rule$

Risk Object Risk Object Type Risk Score Threat Objects
src_ip system 25 EVE_Process, url

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: 2