Detection: Cisco Secure Firewall - High EVE Threat Confidence

Updated Date: 2025-04-02 ID: 8c15183e-2e70-4db4-86c3-88f8d9129b66 Author: Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects connections with a high Encrypted Visibility Engine (EVE) threat confidence score, indicating potentially malicious behavior within encrypted traffic. It leverages Cisco Secure Firewall Threat Defense logs and evaluates the EVE_ThreatConfidencePct field, which reflects the system's confidence in classifying encrypted sessions as threats based on machine learning models and behavioral analysis. A score equal to or greater than 80 suggests the connection is highly likely to be associated with malware command and control (C2), remote access tools, or suspicious tunneling behavior. If confirmed malicious, this may indicate covert communication over TLS from compromised hosts.

 1`cisco_secure_firewall` EventType=ConnectionEvent EVE_ThreatConfidencePct >= 80
 2
 3| stats count min(_time) as firstTime max(_time) as lastTime
 4    Values(rule) as rule
 5    Values(url) as url
 6    by EVE_Process, EVE_ThreatConfidencePct, src_ip, dest, dest_port, transport, action
 7
 8| `security_content_ctime(firstTime)`
 9
10| `security_content_ctime(lastTime)`
11
12| `cisco_secure_firewall___high_eve_threat_confidence_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___high_eve_threat_confidence_filter search *
cisco_secure_firewall___high_eve_threat_confidence_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
T1041 Exfiltration Over C2 Channel Exfiltration
T1071.001 Web Protocols Command And Control
T1105 Ingress Tool Transfer Command And Control
T1573.002 Asymmetric Cryptography Command And Control
Actions on Objectives
Command and Control
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

Some benign applications may exhibit behaviors that resemble encrypted threat patterns, especially if they use uncommon encryption libraries or custom protocols. Custom-developed or internal tools may trigger high EVE confidence scores depending on how they encrypt data. It is recommended to validate the associated process (EVE_Process) and destination context, and correlate with other logs (e.g., endpoint or threat intel) before taking response action.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

High threat confidence ($EVE_ThreatConfidencePct$%) from $EVE_Process$ on $src_ip$"

Risk Object Risk Object Type Risk Score Threat Objects
src_ip system 20 EVE_Process

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