Detection: Cisco NVM - Curl Execution With Insecure Flags

Description

This analytic detects the use of curl.exe with insecure flags such as -k, --insecure, --proxy-insecure, or --doh-insecure which disable TLS certificate validation. It leverages Cisco Network Visibility Module (NVM) flow data and process arguments to identify outbound connections initiated by curl where TLS checks were explicitly disabled. This behavior may indicate an attempt to bypass certificate validation to connect to potentially untrusted or malicious endpoints, a common tactic in red team operations, malware staging, or data exfiltration over HTTPS.

Search

 1`cisco_network_visibility_module_flowdata`
 2process_name = "curl.exe"
 3NOT dest IN (
 4        "10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16", "100.64.0.0/10", 
 5        "127.0.0.0/8", "169.254.0.0/16", "192.0.0.0/24", "192.0.0.0/29", "192.0.0.8/32", 
 6        "192.0.0.9/32", "192.0.0.10/32", "192.0.0.170/32", "192.0.0.171/32", "192.0.2.0/24", 
 7        "192.31.196.0/24", "192.52.193.0/24", "192.88.99.0/24", "224.0.0.0/4", "192.175.48.0/24", 
 8        "198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1"
 9        )
10
11| regex process_arguments="(?i)(?<!\w)-(?:[a-z]*k[a-z]*
12|-(insecure
13|proxy-insecure
14|doh-insecure))"
15
16| stats count min(_time) as firstTime max(_time) as lastTime
17        values(parent_process_arguments) as parent_process_arguments
18        values(process_arguments) as process_arguments
19        values(parent_process_hash) as parent_process_hash
20        values(process_hash) as process_hash
21        values(module_name_list) as module_name_list
22        values(module_hash_list) as module_hash_list
23        values(dest_port) as dest_port
24        values(aliul) as additional_logged_in_users_list
25        values(dest_hostname) as dest_hostname
26        by src dest parent_process_path parent_process_integrity_level process_path process_name process_integrity_level process_id transport
27
28| `security_content_ctime(firstTime)`
29
30| `security_content_ctime(lastTime)`
31
32| table
33  parent_process_integrity_level parent_process_path parent_process_arguments parent_process_hash
34  process_integrity_level process_path process_name process_arguments process_hash process_id
35  additional_logged_in_users_list module_name_list module_hash_list
36  src dest_hostname dest dest_port transport firstTime lastTime
37
38| `cisco_nvm___curl_execution_with_insecure_flags_filter`

Data Source

Name	Platform	Sourcetype	Source
Cisco Network Visibility Module Flow Data	Network	'cisco:nvm:flowdata'	'not_applicable'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

This search requires Network Visibility Module logs, which includes the flow data sourcetype. This search uses an input macro named cisco_network_visibility_module_flowdata. We strongly recommend that you specify your environment-specific configurations (index, source, sourcetype, etc.) for Cisco Network Visibility Module 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 Endpoint Security Analytics (CESA) (https://splunkbase.splunk.com/app/4221).

Known False Positives

Usage of these flags to reach public IPs or uncommon destinations should be reviewed. Tuning may be required for domains with known certificate issues.

Associated Analytic Story

• Cisco Network Visibility Module Analytics

Risk Based Analytics (RBA)

Risk Message:

The host $src$ executed curl with insecure flags and communicated with $dest$ / $dest_hostname$ over port $dest_port$

References

• https://thedfirreport.com/2025/05/19/another-confluence-bites-the-dust-falling-to-elpaco-team-ransomware/

Detection Testing

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