Vulnerability Discussion

Loading and accessing the packet filters programs and maps using the bpf() system call has the potential of revealing sensitive information about the kernel state.

Satisfies: SRG-OS-000132-GPOS-00067, SRG-OS-000480-GPOS-00227

Check

Verify RHEL 9 prevents privilege escalation thru the kernel by disabling access to the bpf system call with the following commands:

$ sysctl kernel.unprivileged_bpf_disabled

kernel.unprivileged_bpf_disabled = 1

If the returned line does not have a value of "1", or a line is not returned, this is a finding.

Check that the configuration files are present to enable this kernel parameter.

$ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|;)' | grep -F kernel.unprivileged_bpf_disabled | tail -1
kernel.unprivileged_bpf_disabled = 1

If the network parameter "ipv4.tcp_syncookies" is not equal to "1", or nothing is returned, this is a finding.

Fix

Configure RHEL 9 to prevent privilege escalation thru the kernel by disabling access to the bpf syscall by adding the following line to a file, in the "/etc/sysctl.d" directory:

kernel.unprivileged_bpf_disabled = 1

The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command:

$ sudo sysctl --system