Techniques
Sample rules
Cisco NVM - Curl Execution With Insecure Flags
- source: splunk
- technicques:
- T1197
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.
Detection logic
`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`