Detection: Cisco Secure Firewall - Bits Network Activity

Description

The following analytic detects the use of the Background Intelligent Transfer Service (BITS) client application in allowed outbound connections. It leverages logs from Cisco Secure Firewall Threat Defense devices and identifies instances where BITS is used to initiate downloads from non-standard or unexpected domains. While BITS is a legitimate Windows service used for downloading updates, it is also commonly abused by adversaries to stealthily retrieve payloads or tools. This analytic filters out known Microsoft Edge update URLs and focuses on connections that may indicate suspicious or unauthorized file transfers. If confirmed malicious, this could represent a command and control (C2) channel or a download of malware or tooling as part of an attack chain.

Search

1`cisco_secure_firewall` EventType=ConnectionEvent action=Allow ClientApplication="BITS" AND NOT url IN ("*://msedge.b.tlu.dl*")
2
3| stats count min(_time) as firstTime max(_time) as lastTime by src_ip, dest, dest_port, transport, rule, url, EVE_Process, ClientApplication, ClientApplicationVersion, action
4
5| `security_content_ctime(firstTime)` 
6
7| `security_content_ctime(lastTime)` 
8
9| `cisco_secure_firewall___bits_network_activity_filter`

Data Source

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 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

BITS is a legitimate Windows component used by Microsoft services such as Windows Update or Microsoft Edge for downloading updates. Although this analytic filters known Microsoft Edge update URLs, false positives may still occur from other legitimate enterprise applications or software distribution platforms that utilize BITS. Additional tuning may be required to account for internal application distribution systems or approved update mechanisms that also rely on BITS.

Associated Analytic Story

• Cisco Secure Firewall Threat Defense Analytics

Risk Based Analytics (RBA)

Risk Message:

$src_ip$ downloaded a file from $url$ via BITS Service

References

• https://www.cisco.com/c/en/us/td/docs/security/firepower/741/api/FQE/secure_firewall_estreamer_fqe_guide_740.pdf

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: 2