Cisco ASA - Core Syslog Message Volume Drop
Last updated 2 days ago on 2026-07-17
About
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.
- Platform
Splunk
- Tags
- Data Source: SplunkDomain: ApplicationRule Type: QueryOS: Any
- Severity
- medium
- Risk Score
- 47
- References
- https://blog.talosintelligence.com/arcanedoor-new-espionage-focused-campaign-found-targeting-perimeter-network-devices/(external, opens in a new tab or window)https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks(external, opens in a new tab or window)https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-z5xP8EUB(external, opens in a new tab or window)https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-http-code-exec-WmfP3h3O(external, opens in a new tab or window)https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-YROOTUW(external, opens in a new tab or window)https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-http-code-exec-WmfP3h3O(external, opens in a new tab or window)https://www.cisa.gov/news-events/directives/ed-25-03-identify-and-mitigate-potential-compromise-cisco-devices(external, opens in a new tab or window)https://www.ncsc.gov.uk/news/persistent-malicious-targeting-cisco-devices(external, opens in a new tab or window)
- 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.
- Source
- View on GitHub(external, opens in a new tab or window)
Definition
- Rule Language
- SPL
- Rule Type
- query
text code block:`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`
View this rule on Splunk
This rule was sourced from the official Splunk public repository. View the original rule on GitHub(external, opens in a new tab or window).