Detection: Cisco Secure Firewall - Wget or Curl Download

Updated Date: 2025-05-02 ID: 173a1cb9-1814-4128-a9dc-f29dade89957 Author: Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects outbound connections initiated by command-line tools such as curl or wget. It leverages Cisco Secure Firewall Threat Defense logs and identifies allowed connections (action=Allow) where either the EVE_Process or ClientApplication fields indicate use of these utilities. While curl and wget are legitimate tools commonly used for software updates and scripting, adversaries often abuse them to download payloads, retrieve additional tools, or establish staging infrastructure from compromised systems. If confirmed malicious, this behavior may indicate the download phase of an attack chain or a command-and-control utility retrieval.

 1`cisco_secure_firewall` EventType=ConnectionEvent action=Allow AND ( EVE_Process IN ("*curl*", "*wget*") OR ClientApplication IN ("cURL", "Wget") )
 2
 3| stats count min(_time) as firstTime max(_time) as lastTime
 4    Values(rule) as rule
 5    Values(url) as url
 6    Values(dest_port) as dest_port
 7    Values(ClientApplicationVersion) as ClientApplicationVersion
 8    Values(src_port) as src_port
 9    by src_ip, dest, transport, EVE_Process, ClientApplication, action
10
11| table src_ip src_port dest dest_port transport url EVE_Process ClientApplication ClientApplicationVersion rule firstTime lastTime
12
13| `security_content_ctime(firstTime)`
14
15| `security_content_ctime(lastTime)` 
16
17| `cisco_secure_firewall___wget_or_curl_download_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___wget_or_curl_download_filter search *
cisco_secure_firewall___wget_or_curl_download_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
T1053.003 Cron Execution
T1059 Command and Scripting Interpreter Persistence
T1071.001 Web Protocols Privilege Escalation
T1105 Ingress Tool Transfer Execution
Command and Control
Exploitation
Installation
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

Developers, administrators, or automation tools may use curl or wget for legitimate purposes such as software installation, configuration scripts, or CI/CD tasks. Security tools or health monitoring scripts may also use these utilities to check service availability or download updates. Review the destination url, frequency, and process context to validate whether the download activity is authorized.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The process $EVE_Process$ initiated an allowed connection to download content using a command-line utility ($ClientApplication$) from $url$. This behavior may indicate tool staging or payload retrieval via curl or wget.

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