Zscaler Virus Download threat blocked

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.

Query · spl

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

Implementation guide

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.

Analyst notes

Known false positives: False positives are limited to Zscaler configuration.

Raw source Zscaler Virus Download threat blocked · SPL
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Published by splunk/security_content ↗, licensed under Apache 2.0 ↗. Reproduced here unmodified. 
name: Zscaler Virus Download threat blocked
id: aa19e627-d448-4a31-85cd-82068dec5691
version: 10
creation_date: '2024-04-17'
modification_date: '2026-05-13'
author: Gowthamaraj Rajendran, Rod Soto, Splunk
status: production
type: Anomaly
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.
data_source: []
search: |-
    `zscaler_proxy` action=blocked threatname!="None" threatclass=Virus
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY action deviceowner user
           urlcategory url src
           dest
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `zscaler_virus_download_threat_blocked_filter`
how_to_implement: 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.
references:
    - https://help.zscaler.com/zia/nss-feed-output-format-web-logs
drilldown_searches:
    - name: View the detection results for - "$src$" and "$user$"
      search: '%original_detection_search% | search  src = "$src$" user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$src$" and "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src$", "$user$") | 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: Potential Virus Download Threat from dest -[$dest$] on $src$ for user-[$user$].
        - field: user
          type: user
          score: 20
          message: Potential Virus Download Threat from dest -[$dest$] on $src$ for user-[$user$].
threat_objects:
    - field: url
      type: url
analytic_story:
    - Zscaler Browser Proxy Threats
asset_type: Web Server
mitre_attack_id:
    - T1566
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: web
security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1566/zscalar_web_proxy/zscalar_web_proxy.json
          source: zscaler
          sourcetype: zscalernss-web
      test_type: unit

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