Detection: Cisco Secure Firewall - File Download Over Uncommon Port

Updated Date: 2025-05-02 ID: f26445a8-a6a2-4855-bec0-0c39e52e5b8f Author: Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects file transfers flagged as malware that occurred over non-standard ports (other than 80 and 443). Adversaries may attempt to bypass protocol-based detection or use alternate ports to blend in with other traffic. This analytic identifies these non-conventional flows and surfaces potential evasion techniques. If confirmed malicious this indicate potential malware delivery or other nefarious activity.

 1`cisco_secure_firewall` EventType=FileEvent FileDirection="Download" NOT dest_port IN (80, 443)
 2
 3| lookup cisco_secure_firewall_filetype_lookup Name as FileType OUTPUT Description
 4
 5| stats count min(_time) as firstTime max(_time) as lastTime 
 6        values(file_name) as file_name 
 7        values(uri) as uri 
 8        values(ClientApplication) as ClientApplication
 9        values(file_hash) as file_hash 
10        values(SHA_Disposition) as SHA_Disposition 
11        by FileDirection FileType app ThreatName dest_port Description src_ip dest
12
13| `security_content_ctime(firstTime)`
14
15| `security_content_ctime(lastTime)`
16
17| table firstTime lastTime src_ip dest dest_port FileDirection FileType Description uri ClientApplication file_name file_hash SHA_Disposition ThreatName
18
19| `cisco_secure_firewall___file_download_over_uncommon_port_filter`

Data Source

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

Macros Used

Name Value
cisco_secure_firewall sourcetype="cisco:sfw:estreamer"
cisco_secure_firewall___file_download_over_uncommon_port_filter search *
cisco_secure_firewall___file_download_over_uncommon_port_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
T1105 Ingress Tool Transfer Command And Control
T1571 Non-Standard Port Command And Control
Command and Control
DE.AE
CIS 10

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 FileEvent 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 malware & file access policy must also enable logging.

Known False Positives

Some legitimate applications may download files over custom ports (e.g., CDN mirrors, APIs). Apply additional filters accordingly.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The host $src_ip$ downloaded a file $file_name$ of type $FileType$ from $dest$ over the uncommon port $dest_port$

Risk Object Risk Object Type Risk Score Threat Objects
src_ip system 30 file_hash, file_name

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