Excessive DNS Failures

Status: experimental
Severity: low
Group by: "DNS.query", "DNS.reply_code", "DNS.src", reply_code, src
Author: bowesmana, Bhavin Patel, Splunk
Source: github.com/splunk/security_content

The following analytic identifies excessive DNS query failures by counting DNS responses that do not indicate success, triggering when there are more than 50 occurrences. It leverages the Network_Resolution data model, focusing on DNS reply codes that signify errors. This activity is significant because a high number of DNS failures can indicate potential network misconfigurations, DNS poisoning attempts, or malware communication issues. If confirmed malicious, this activity could lead to disrupted network services, hindered communication, or data exfiltration attempts by attackers.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1071.004` Application Layer Protocol: DNS

Rule body splunk

name: Excessive DNS Failures
id: 104658f4-afdc-499e-9719-17243f9826f1
version: 11
creation_date: '2019-10-16'
modification_date: '2026-05-13'
author: bowesmana, Bhavin Patel, Splunk
status: experimental
type: Anomaly
description: The following analytic identifies excessive DNS query failures by counting DNS responses that do not indicate success, triggering when there are more than 50 occurrences. It leverages the Network_Resolution data model, focusing on DNS reply codes that signify errors. This activity is significant because a high number of DNS failures can indicate potential network misconfigurations, DNS poisoning attempts, or malware communication issues. If confirmed malicious, this activity could lead to disrupted network services, hindered communication, or data exfiltration attempts by attackers.
data_source: []
search: |-
    | 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`
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.
references: []
intermediate_findings:
    entities:
        - field: src
          type: system
          score: 20
          message: Excessive DNS failures detected on $src$
analytic_story:
    - Suspicious DNS Traffic
    - Command And Control
asset_type: Endpoint
mitre_attack_id:
    - T1071.004
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: network
security_domain: network

Stages and Predicates

Stage 1: `tstats`

| 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"

Stage 2: `search`

| `drop_dm_object_name("DNS")`

Stage 3: `lookup`

| lookup cim_corporate_web_domain_lookup domain as query OUTPUT domain

Lookup table: cim_corporate_web_domain_lookup
Key field: domain as query
Output columns: ['domain', 'domain']

Stage 4: `where`

| where isnull(domain)

Stage 5: `lookup`

| lookup update=true alexa_lookup_by_str domain as query OUTPUT rank

Lookup table: alexa_lookup_by_str
Key field: domain as query
Output columns: ['rank', 'rank']

Stage 6: `where`

| where isnull(rank)

Stage 7: `eventstats`

| eventstats max(count) as mc
  BY src reply_code

Stage 8: `eval`

| eval mode_query=if(count=mc, query, null())

Stage 9: `stats`

| stats sum(count) as count values(mode_query) as query values(mc) as max_query_count
  BY src reply_code

Stage 10: `where`

| where count>50

Stage 11: `search`

| `get_asset(src)`

Stage 12: `search`

| `excessive_dns_failures_filter`

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`"DNS.query"`	eq	`"*.arpa"`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`"DNS.query"`	eq	`"."`
`"DNS.reply_code"`	ne	`"No Error"` `"NoError"`
`DNS.reply_code`	ne	`"unknown"`
`count`	gt	`50`
`domain`	is_null	(no value, null check)
`nodename`	eq	`DNS`
`rank`	is_null	(no value, null check)

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Excessive DNS Failures

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: `tstats`

Stage 2: `search`

Stage 3: `lookup`

Stage 4: `where`

Stage 5: `lookup`

Stage 6: `where`

Stage 7: `eventstats`

Stage 8: `eval`

Stage 9: `stats`

Stage 10: `where`

Stage 11: `search`

Stage 12: `search`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Excessive DNS Failures

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: tstats

Stage 2: search

Stage 3: lookup

Stage 4: where

Stage 5: lookup

Stage 6: where

Stage 7: eventstats

Stage 8: eval

Stage 9: stats

Stage 10: where

Stage 11: search

Stage 12: search

Exclusions

Indicators

Stage 1: `tstats`

Stage 2: `search`

Stage 3: `lookup`

Stage 4: `where`

Stage 5: `lookup`

Stage 6: `where`

Stage 7: `eventstats`

Stage 8: `eval`

Stage 9: `stats`

Stage 10: `where`

Stage 11: `search`

Stage 12: `search`