LoFP / a elasticache security group deletion may be done by a system or network administrator. verify whether the user identity, user agent, and/or hostname should be making changes in your environment. security group deletions by unfamiliar users or hosts should be investigated. if known behavior is causing false positives, it can be exempted from the rule.

event.dataset:aws.cloudtrail and event.provider:elasticache.amazonaws.com and event.action:("Delete Cache Security Group" or
"Authorize Cache Security Group Ingress" or  "Revoke Cache Security Group Ingress" or "AuthorizeCacheSecurityGroupEgress" or
"RevokeCacheSecurityGroupEgress") and event.outcome:success

condition: selection
selection:
  eventName:
  - DeleteCacheSecurityGroup
  - AuthorizeCacheSecurityGroupIngress
  - RevokeCacheSecurityGroupIngress
  - AuthorizeCacheSecurityGroupEgress
  - RevokeCacheSecurityGroupEgress
  eventSource: elasticache.amazonaws.com