splunk-security_content/docs/_posts/2020-07-21-excessive_dns_failures.md

title, excerpt, categories, last_modified_at, toc, toc_label, tags

title	excerpt	categories	last_modified_at	toc	toc_label	tags
Excessive DNS Failures	DNS, Application Layer Protocol	Network	2020-07-21	true		DNS Command And Control Application Layer Protocol Command And Control Splunk Enterprise Splunk Enterprise Security Splunk Cloud Network_Resolution

⚠️ WARNING THIS IS A EXPERIMENTAL DETECTION

We have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

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Description

This search identifies DNS query failures by counting the number of DNS responses that do not indicate success, and trigger on more than 50 occurrences.

• Type: Anomaly
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Network_Resolution
• Last Updated: 2020-07-21
• Author: Bhavin Patel, Splunk
• ID: 104658f4-afdc-499e-9719-17243f9826f1

ATT&CK

ID	Technique	Tactic
T1071.004	DNS	Command And Control

| T1071 | Application Layer Protocol | Command And Control |

Search

| tstats `security_content_summariesonly` count values("DNS.query") as queries from datamodel=Network_Resolution where nodename=DNS "DNS.reply_code"!="No Error" "DNS.reply_code"!="NoError" DNS.reply_code!="unknown" NOT "DNS.query"="*.arpa" "DNS.query"="*.*" by "DNS.src","DNS.query"
| `drop_dm_object_name("DNS")`
| lookup cim_corporate_web_domain_lookup domain as query OUTPUT domain
| where isnull(domain)
| lookup update=true alexa_lookup_by_str domain as query OUTPUT rank
| where isnull(rank)
| stats sum(count) as count mode(queries) as queries by src
| `get_asset(src)`
| where count>50 
| `excessive_dns_failures_filter`

Associated Analytic Story

• Suspicious DNS Traffic
• Command and Control

How To Implement

To successfully implement this search you must ensure that DNS data is populating the Network_Resolution data model.

Required field

• _time
• DNS.query
• DNS.reply_code
• DNS.src

Kill Chain Phase

• Command and Control

Known False Positives

It is possible legitimate traffic can trigger this rule. Please investigate as appropriate. The threshold for generating an event can also be customized to better suit your environment.

Reference

Test Dataset

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

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