Detection: Zscaler Virus Download threat blocked

Updated Date: 2024-09-30 ID: aa19e627-d448-4a31-85cd-82068dec5691 Author: Gowthamaraj Rajendran, Rod Soto, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies attempts to download viruses that were blocked by Zscaler within a network. It leverages web proxy logs to detect blocked actions indicative of virus download attempts. Key data points such as device owner, user, URL category, destination URL, and IP are analyzed. This activity is significant as it helps in early detection and remediation of potential virus threats, enhancing network security. If confirmed malicious, this activity could indicate an attempt to compromise the network, potentially leading to data breaches or further malware infections.

Search

1`zscaler_proxy` action=blocked threatname!="None" threatclass=Virus 
2| stats count min(_time) as firstTime max(_time) as lastTime by action deviceowner user urlcategory url src dest 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `zscaler_virus_download_threat_blocked_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
zscaler_virus_download_threat_blocked_filter	`search *`

zscaler_virus_download_threat_blocked_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1566	Phishing	Initial Access

KillChainPhase.DELIVERY

NistCategory.DE_AE

Cis18Value.CIS_10

Axiom

GOLD SOUTHFIELD

INC Ransom

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

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

You must install the latest version of Zscaler Add-on from Splunkbase. You must be ingesting Zscaler events into your Splunk environment through an ingester. This analytic was written to be used with the "zscalernss-web" sourcetype leveraging the Zscaler proxy data. This enables the integration with Splunk Enterprise Security. Security teams are encouraged to adjust the detection parameters, ensuring the detection is tailored to their specific environment.

Known False Positives

False positives are limited to Zscaler configuration.

Associated Analytic Story

Zscaler Browser Proxy Threats

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Potential Virus Download Threat from dest -[$dest$] on $src$ for user-[$user$].	40	50	80

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

https://help.zscaler.com/zia/nss-feed-output-format-web-logs

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`zscaler`	`zscalernss-web`
Integration	✅ Passing	Dataset	`zscaler`	`zscalernss-web`

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: 3