Excessive DNS Failures
THIS IS A EXPERIMENTAL DETECTION
This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.
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: 2022-12-21
- Author: bowesmana, Bhavin Patel, Splunk
- ID: 104658f4-afdc-499e-9719-17243f9826f1
Kill Chain Phase
- Command and Control
- CIS 13
1 2 3 4 5 6 7 8 9 10 11 12 13 | tstats `security_content_summariesonly` count 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" "DNS.reply_code" | `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) | eventstats max(count) as mc by src reply_code | eval mode_query=if(count=mc, query, null()) | stats sum(count) as count values(mode_query) as query values(mc) as max_query_count by src reply_code | where count>50 | `get_asset(src)` | `excessive_dns_failures_filter`
The SPL above uses the following Macros:
excessive_dns_failures_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
To successfully implement this search you must ensure that DNS data is populating the Network_Resolution data model.
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.
Associated Analytic Story
|25.0||50||50||Excessive DNS failures detected on $src$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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source | version: 3