ID | Technique | Tactic |
---|---|---|
T1018 | Remote System Discovery | Discovery |
T1046 | Network Service Discovery | Discovery |
T1110 | Brute Force | Credential Access |
T1203 | Exploitation for Client Execution | Execution |
T1595.002 | Vulnerability Scanning | Reconnaissance |
Detection: Cisco Secure Firewall - Repeated Blocked Connections
Description
The following analytic detects repeated blocked connection attempts from the same initiator to the same responder within a short time window. It leverages Cisco Secure Firewall Threat Defense logs and identifies connections where the action is set to Block, and the number of occurrences reaches or exceeds a threshold of ten within a one-minute span. This pattern may indicate a misconfigured application, unauthorized access attempts, or early stages of a brute-force or scanning operation. If confirmed malicious, this behavior may represent an attacker probing the network, attempting lateral movement, or testing firewall rules for weaknesses.
Search
1`cisco_secure_firewall` EventType=ConnectionEvent action=Block
2
3| bin _time span=1m
4
5| stats count min(_time) as firstTime max(_time) as lastTime
6 Values(dest_port) as dest_port
7 Values(url) as url
8 by src_ip, dest, transport, rule, action
9
10| where count >= 10
11
12| `security_content_ctime(firstTime)`
13
14| `security_content_ctime(lastTime)`
15
16| `cisco_secure_firewall___repeated_blocked_connections_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___repeated_blocked_connections_filter | search * |
cisco_secure_firewall___repeated_blocked_connections_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
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
Misconfigured applications or automated scripts may generate repeated blocked traffic, particularly if attempting to reach decommissioned or restricted resources. Vulnerability scanners or penetration testing tools running in authorized environments may trigger this alert. Tuning may be required to exclude known internal tools or scanner IPs from detection.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message:
Repeated blocked connections detected from $src_ip$ to $dest$ according to the configured firewall rule $rule$
Risk Object | Risk Object Type | Risk Score | Threat Objects |
---|---|---|---|
src_ip | system | 25 | 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: 1