Cisco ASA - Core Syslog Message Volume Drop

Status: production
Group by: _time, message_id
Author: Bhavin Patel, Micheal Haag, Splunk
Source: github.com/splunk/security_content

Adversaries may intentionally suppress or reduce the volume of core Cisco ASA syslog messages to evade detection or cover their tracks. This hunting search is recommended to proactively identify suspicious downward shifts or absences in key syslog message IDs, which may indicate tampering or malicious activity. Visualizing this data in Splunk dashboards enables security teams to quickly spot anomalies and investigate potential compromise.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	`T1685` Disable or Modify Tools

Rule body splunk

name: Cisco ASA - Core Syslog Message Volume Drop
id: 4b4f8fdd-1f9e-45d8-9b0f-1f64c0b297a4
version: 5
creation_date: '2025-09-25'
modification_date: '2026-05-13'
author: Bhavin Patel, Micheal Haag, Splunk
status: production
type: Hunting
description: |
    Adversaries may intentionally suppress or reduce the volume of core Cisco ASA syslog messages to evade detection or cover their tracks. This hunting search is recommended to proactively identify suspicious downward shifts or absences in key syslog message IDs, which may indicate tampering or malicious activity. Visualizing this data in Splunk dashboards enables security teams to quickly spot anomalies and investigate potential compromise.
data_source:
    - Cisco ASA Logs
search: |
    `cisco_asa`
    message_id IN (302013, 302014, 609002, 710005)
    | eval msg_desc=case(
      message_id="302013","Built inbound TCP connection",
      message_id="302014","Teardown TCP connection",
      message_id="609002","Teardown local-host management",
      message_id="710005","TCP request discarded"
    )
    | bin _time span=15m
    | stats count values(msg_desc) as message_description
                  values(dest) as dest
      by _time message_id
    | xyseries _time message_id count
    | `cisco_asa___core_syslog_message_volume_drop_filter`
how_to_implement: |
    This search requires Cisco ASA syslog data to be ingested into Splunk via the Cisco Security Cloud TA. To ensure this detection works effectively, configure your ASA and FTD devices to generate and forward both debug and informational level syslog messages before they are sent to Splunk.
    This analytic is designed to be used with comprehensive logging enabled, as it relies on the presence of specific message IDs. You can find specific instructions on how to set this up here : https://www.cisco.com/c/en/us/support/docs/security/pix-500-series-security-appliances/63884-config-asa-00.html#toc-hId--1451069880.
    The search produces a time-series suitable for dashboards to visualize drops across message IDs 302013, 302014, 609002, and 710005.
    You can also change the severity level of the above message id's to the syslog level you have currently enabled using the logging message syslog_id level severity_level command in global configuration mode. For more information, see Change the Severity Level of a Syslog Message : https://www.cisco.com/c/en/us/td/docs/security/asa/asa922/configuration/general/asa-922-general-config/monitor-syslog.html#ID-2121-000006da
known_false_positives: |
    Planned maintenance, network outages, routing changes, or benign configuration updates may reduce log volume temporarily.
    Validate against change management records and corroborate with device health metrics.
references:
    - https://blog.talosintelligence.com/arcanedoor-new-espionage-focused-campaign-found-targeting-perimeter-network-devices/
    - https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks
    - https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-z5xP8EUB
    - https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-http-code-exec-WmfP3h3O
    - https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-YROOTUW
    - https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-http-code-exec-WmfP3h3O
    - https://www.cisa.gov/news-events/directives/ed-25-03-identify-and-mitigate-potential-compromise-cisco-devices
    - https://www.ncsc.gov.uk/news/persistent-malicious-targeting-cisco-devices
analytic_story:
    - Suspicious Cisco Adaptive Security Appliance Activity
    - ArcaneDoor
asset_type: Network
cve:
    - CVE-2025-20333
    - CVE-2025-20362
mitre_attack_id:
    - T1685
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: application
security_domain: network
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_asa/arcane_door/cisco_asa.log
          source: not_applicable
          sourcetype: cisco:asa
      test_type: unit

Stages and Predicates

Stage 1: `search`

`cisco_asa`
message_id IN (302013, 302014, 609002, 710005)

Stage 2: `eval`

| eval msg_desc=case(
  message_id="302013","Built inbound TCP connection",
  message_id="302014","Teardown TCP connection",
  message_id="609002","Teardown local-host management",
  message_id="710005","TCP request discarded"
)

msg_desc =

ifmessage_id = "302013""Built inbound TCP connection"

elifmessage_id = "302014""Teardown TCP connection"

elifmessage_id = "609002""Teardown local-host management"

else"TCP request discarded"

Stage 3: `bucket`

| bin _time span=15m

Stage 4: `stats`

| stats count values(msg_desc) as message_description
              values(dest) as dest
  by _time message_id

Stage 5: `search`

| xyseries _time message_id count

Stage 6: `search`

| `cisco_asa___core_syslog_message_volume_drop_filter`

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
`message_id`	in	`302013` `302014` `609002` `710005`
`sourcetype`	eq	`cisco:asa`

Search terms

Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.

Stage	Term
5	`xyseries`
5	`message_id`
5	`count`

`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)

Cisco ASA - Core Syslog Message Volume Drop

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: `search`

Stage 2: `eval`

Stage 3: `bucket`

Stage 4: `stats`

Stage 5: `search`

Stage 6: `search`

Indicators

Search terms

Keyboard shortcuts

Search operators

Cisco ASA - Core Syslog Message Volume Drop

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: search

Stage 2: eval

Stage 3: bucket

Stage 4: stats

Stage 5: search

Stage 6: search

Indicators

Search terms

Stage 1: `search`

Stage 2: `eval`

Stage 3: `bucket`

Stage 4: `stats`

Stage 5: `search`

Stage 6: `search`