Log Modification

The Principle of Least Privilege should be enforced, and period reviews of permissions conducted to ensure that accounts have the minimum level of access required to complete duties as per their role.

An agent capable of Endpoint Detection and Response (EDR) is a software agent installed on organization endpoints (such as laptops and servers) that (at a minimum) records the Operating System, application, and network activity on an endpoint.

Typically EDR operates in an agent/server model, where agents automatically send logs to a server, where the server correlates those logs based on a rule set. This rule set is then used to surface potential security-related events, that can then be analyzed.

An EDR agent typically also has some form of remote shell capability, where a user of the EDR platform can gain a remote shell session on a target endpoint, for incident response purposes. An EDR agent will typically have the ability to remotely isolate an endpoint, where all network activity is blocked on the target endpoint (other than the network activity required for the EDR platform to operate).

An agent capable of User Activity Monitoring (UAM) is a software agent installed on organization endpoints (such as laptops); typically, User Activity Monitoring agents are only deployed on endpoints where a human user Is expected to conduct the activity.

The User Activity Monitoring agent will typically record Operating System, application, and network activity occurring on an endpoint, with a focus on activity that is or can be conducted by a human user. The purpose of this monitoring is to identify undesirable and/or malicious activity being conducted by a human user (in this context, an Insider Threat).

Typical User Activity Monitoring platforms operate in an agent/server model where activity logs are sent to a server for automatic correlation against a rule set. This rule set is used to surface activity that may represent Insider Threat related activity such as capturing screenshots, copying data, compressing files or installing risky software.

Other platforms providing related functionality are frequently referred to as User Behaviour Analytics (UBA) platforms.

An agent capable of User Behaviour Analytics (UBA) is a software agent installed on organizational endpoints (such as laptops). Typically, User Activity Monitoring agents are only deployed on endpoints where a human user is expected to conduct the activity.

The User Behaviour Analytics agent will typically record Operating System, application, and network activity occurring on an endpoint, focusing on activity that is or can be conducted by a human user. Typically, User Behaviour Analytics platforms operate in an agent/server model where activity logs are sent to a server for automatic analysis. In the case of User Behaviour Analytics, this analysis will typically be conducted against a baseline that has previously been established.

A User Behaviour Analytic platform will typically conduct a period of ‘baselining’ when the platform is first installed. This baselining period establishes the normal behavior parameters for an organization’s users, which are used to train a Machine Learning (ML) model. This ML model can then be later used to automatically identify activity that is predicted to be an anomaly, which is hoped to surface user behavior that is undesirable, risky, or malicious.

Other platforms providing related functionality are frequently referred to as User Activity Monitoring (UAM) platforms.

Audit Daemon (auditd) is a powerful tool in Linux for tracking and logging system events, including file access. It’s part of the Linux Auditing System, which provides detailed and customizable logging of various types of system activity.

Below is an example auditd rule to detect timestamp modification:

sudo nano /etc/audit/rules.d/audit.rules
Opens the auditd rules file with the Nano editor. Add the following line:

-a always,exit -F arch=b64 -S utimensat -F key=timestamp-changed

-a Add a rule to the audit system

always,exit Apply this rule to both the entry and exit points of the system call. It means that audit records will be generated both when the system call starts and when it ends

-F arch=b64 Filter condition. Specifies that this rule applies to 64-bit architecture (this can be replaced with -F arch=b32)

-S utimensat Specifies the utimensat system call to be audited

-F key=timestamp-changed Adds a key to the rule for easier identification in the logs

To review audit logs related to this rule, we can use ausearch (ausearch -k timestamp-changed) or read and retrieve lines from the raw audit logs with grep (sudo grep timestamp-changed /var/log/audit/audit.log).

This detection is not enabled by default and requires additional configuration.

System Monitor (Sysmon) Event ID 1 is used to record process execution. Reviewing these logs can determine what software has been run on a system.

By autonomously collecting log files from a system and transporting them to another system, such as a SIEM collector, they are typically no longer accessible by the subject, preventing them from being able to delete them. These can aid in investigations where a subject has deleted local logs.