The following analytic identifies a suspicious file creation of /etc/at.allow or /etc/at.deny. These 2 files are commonly abused by malware, adversaries or red teamers to persist on the targeted or compromised host. These config files can restrict or allow user to execute “at” application (another schedule task application in linux). attacker can create a user or add the compromised username to that config file to execute “at” to schedule it malicious code. This anomaly detection can be a good indicator to investigate further the entry in created config file and who created it to verify if it is a false positive.
- Type: Anomaly
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-12-17
- Author: Teoderick Contreras, Splunk
- ID: 977b3082-5f3d-11ec-b954-acde48001122
Kill Chain Phase
- CIS 3
- CIS 5
- CIS 16
1 2 3 4 5 6 | tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*/etc/at.allow", "*/etc/at.deny") by Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.process_guid Filesystem.file_path | `drop_dm_object_name(Filesystem)` | `security_content_ctime(lastTime)` | `security_content_ctime(firstTime)` | `linux_at_allow_config_file_creation_filter`
The SPL above uses the following Macros:
linux_at_allow_config_file_creation_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
How To Implement
To successfully implement this search, you need to be ingesting logs with the file name, file path, and process_guid executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase.
Known False Positives
Administrator or network operator can create this file for automation purposes. Please update the filter macros to remove false positives.
Associated Analytic story
|25.0||50||50||A file $file_name$ is created in $file_path$ on $dest$|
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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