Amazon Linux 2023 must audit all uses of the chmod, fchmod, and fchmodat system calls.

Without generating audit records specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.

Audit records can be generated from various components within the information system (e.g., module or policy filter).

When a user logs on, the auid is set to the uid of the account being authenticated. Daemons are not user sessions and have the loginuid set to -1. The auid representation is an unsigned 32-bit integer, which equals 4294967295. The audit system interprets -1, 4294967295, and "unset" in the same way.

The system call rules are loaded into a matching engine that intercepts each system call made by all programs on the system. Therefore, it is very important to use system call rules only when absolutely necessary since these affect performance. The more rules, the bigger the performance hit. The performance can be helped, however, by combining system calls into one rule whenever possible.

Satisfies: SRG-OS-000037-GPOS-00015, SRG-OS-000042-GPOS-00020, SRG-OS-000062-GPOS-00031, SRG-OS-000392-GPOS-00172, SRG-OS-000462-GPOS-00206, SRG-OS-000471-GPOS-00215, SRG-OS-000064-GPOS-00033, SRG-OS-000466-GPOS-00210, SRG-OS-000458-GPOS-00203

Verify Amazon Linux 2023 is configured to audit the execution of the "chmod", "fchmod", and "fchmodat" system calls with the following command:

$ sudo auditctl -l | grep chmod -a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=unset -k perm_mod

If the command does not return the expected line, or the line is commented out, this is a finding.

Configure Amazon Linux 2023 to generate audit records upon successful/unsuccessful attempts to use the "chmod", "fchmod", and "fchmodat" syscalls.

Add or update the following rule in "/etc/audit/rules.d/audit.rules":

-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=unset -k perm_mod

To load the rule to the kernel immediately, use the following command:

$ sudo augenrules --load