The following analytic detects the creation of suspicious configuration files, /etc/at.allow or /etc/at.deny, in Linux. These files are commonly abused by malware, adversaries, or red teamers to establish persistence on compromised hosts. The configuration files determine which users are allowed to execute the "at" application, which is used for scheduling tasks in Linux. Attackers can add their user or a compromised username to these files to execute malicious code using "at." It's important to consider potential false positives as administrators or network operators may create these files for legitimate automation purposes. Adjust the filter macros to minimize false positives.
Identifying the creation of these configuration files is valuable for a SOC as it indicates potential unauthorized activities or an attacker attempting to establish persistence. If a true positive is found, further investigation is necessary to examine the contents of the created configuration file and determine the source of creation. The impact of a true positive can vary but could result in unauthorized execution of malicious code, data theft, or other detrimental consequences. Analysts should review the file path, creation time, and associated processes to assess the extent of the attack and initiate appropriate response actions.
- 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 10
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.
List of fields required to use this analytic.
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 into the Endpoint datamodel. 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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