Detection: Cisco Secure Firewall - Connection to File Sharing Domain

Updated Date: 2025-05-02 ID: f7e5e792-d907-46c1-a58e-4ff974dc462a Author: Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects outbound connections to commonly abused file sharing and pastebin-style hosting domains. It leverages Cisco Secure Firewall Threat Defense logs and focuses on allowed connections (action=Allow) where the url field matches a list of known data hosting or temporary storage services. While many of these platforms serve legitimate purposes, they are frequently leveraged by adversaries for malware delivery, data exfiltration, command and control (C2) beacons, or staging of encoded payloads. This analytic is valuable for identifying potential abuse of legitimate infrastructure as part of an attacker's kill chain. If confirmed malicious, this activity may indicate tool staging, credential dumping, or outbound data leaks over HTTP(S).

 1`cisco_secure_firewall` action=Allow EventType=ConnectionEvent url IN ("*//objects.githubusercontent.com*", "*anonfiles.com*", "*cdn.discordapp.com*", "*ddns.net*", "*dl.dropboxusercontent.com*", "*ghostbin.co*", "*glitch.me*", "*gofile.io*", "*hastebin.com*", "*mediafire.com*", "*mega.nz*", "*onrender.com*", "*pages.dev*", "*paste.ee*", "*pastebin.com*", "*pastebin.pl*", "*pastetext.net*", "*privatlab.com*", "*privatlab.net*", "*send.exploit.in*", "*sendspace.com*", "*storage.googleapis.com*", "*storjshare.io*", "*supabase.co*", "*temp.sh*", "*transfer.sh*", "*trycloudflare.com*", "*ufile.io*", "*w3spaces.com*", "*workers.dev*")
 2
 3| stats count min(_time) as firstTime max(_time) as lastTime 
 4  Values(src_port) as src_port
 5  Values(dest) as dest
 6  Values(dest_port) as dest_port
 7  Values(rule) as rule
 8  Values(url) as url
 9  Values(EVE_Process) as EVE_Process
10  by src_ip, transport, action
11
12| `security_content_ctime(firstTime)` 
13
14| `security_content_ctime(lastTime)` 
15
16| `cisco_secure_firewall___connection_to_file_sharing_domain_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___connection_to_file_sharing_domain_filter search *
cisco_secure_firewall___connection_to_file_sharing_domain_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
T1071.001 Web Protocols Command And Control
T1090.002 External Proxy Command And Control
T1105 Ingress Tool Transfer Command And Control
T1567.002 Exfiltration to Cloud Storage Exfiltration
T1588.002 Tool Resource Development
Actions on Objectives
Command and Control
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 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

Legitimate users and applications may use these domains for benign purposes such as file transfers, collaborative development, or storing public content. Developer tools, browser extensions, or open-source software may connect to githubusercontent.com or cdn.discordapp.com as part of normal operation. It is recommended to review the associated process (EVE_Process), user behavior, and frequency of access before classifying the activity as suspicious.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The host $src_ip$ initiated a connection to the file sharing or pastebin domain $url$.

Risk Object Risk Object Type Risk Score Threat Objects
src_ip system 30 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