Cisco NVM - Curl Execution With Insecure Flags
SPLUNK detection rule by Nasreddine Bencherchali, Splunk · Apache-2.0
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.
name: Cisco NVM - Curl Execution With Insecure Flags
id: cc695238-3117-4e60-aa83-4beac2a42c69
version: 8
creation_date: '2025-07-01'
modification_date: '2026-07-14'
author: Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
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.
data_source:
- Cisco Network Visibility Module Flow Data
search: |
`cisco_network_visibility_module_flowdata`
process_name = "curl.exe"
NOT dest IN (
"10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16", "100.64.0.0/10",
"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",
"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",
"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",
"198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1"
)
| regex process_arguments="(?i)(?<!\w)-(?:[a-z]*k[a-z]*|-(insecure|proxy-insecure|doh-insecure))"
| stats count min(_time) as firstTime max(_time) as lastTime
values(parent_process_arguments) as parent_process_arguments
values(process_arguments) as process_arguments
values(parent_process_hash) as parent_process_hash
values(process_hash) as process_hash
values(module_name_list) as module_name_list
values(module_hash_list) as module_hash_list
values(dest_port) as dest_port
values(aliul) as additional_logged_in_users_list
values(dest_hostname) as dest_hostname
by src dest parent_process_path parent_process_integrity_level process_path process_name process_integrity_level process_id transport
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| table
parent_process_integrity_level parent_process_path parent_process_arguments parent_process_hash
process_integrity_level process_path process_name process_arguments process_hash process_id
additional_logged_in_users_list module_name_list module_hash_list
src dest_hostname dest dest_port transport firstTime lastTime
| `cisco_nvm___curl_execution_with_insecure_flags_filter`
how_to_implement: |
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.
references:
- https://thedfirreport.com/2025/05/19/another-confluence-bites-the-dust-falling-to-elpaco-team-ransomware/
drilldown_searches:
- name: View the detection results for - "$src$"
search: '%original_detection_search% | search src = "$src$"'
earliest_offset: $info_min_time$
latest_offset: $info_max_time$
- name: View risk events for the last 7 days for - "$src$"
search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
earliest_offset: 7d
latest_offset: "0"
intermediate_findings:
entities:
- field: src
type: system
score: 20
message: The host $src$ executed curl with insecure flags and communicated with $dest$ / $dest_hostname$ over port $dest_port$
threat_objects:
- field: process_name
type: process_name
analytic_story:
- Cisco Network Visibility Module Analytics
- PromptLock
- Microsoft WSUS CVE-2025-59287
asset_type: Endpoint
mitre_attack_id:
- T1197
product:
- Splunk Enterprise
- Splunk Enterprise Security
- Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
- name: True Positive Test - Cisco NVM
attack_data:
- data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_network_visibility_module/cisco_nvm_flowdata/nvm_flowdata.log
source: not_applicable
sourcetype: cisco:nvm:flowdata:v2
test_type: unit
CIRCL