OpenSCAP Part 3: Running Scans from the Command Line in RHEL 7

openscap-base

Introduction

In part 1 of this series we were introduced to OpenSCAP and the process of running scans via the SCAP workbench. In part 2, we explored concepts and components that define security/vulnerability scans. In this 3rd post we are going to dive into the command line operation.

Let’s get started with oscap.

Installing oscap

In RHEL 7 oscap can be installed with the following command

# yum -y install scap-security-guide openscap-scanner

Content is installed under the following directory. Note that ssg is short for SCAP Security Guide.

/usr/share/xml/scap/ssg/content

Lets change directories to the one listed above and view the installed files.

Screenshot from 2019-07-24 15-58-04

Using oscap we can view more info on each file shown above. In this example we are going to inspect the ssg-rhel7-ds.xml file.

# oscap info ssg-rhel7-ds.xml

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OpenSCAP Part 2: SCAP Content for RHEL 7

openscap-base

Introduction

In part one of the OpenSCAP series we were introduced to the basic usage of the OpenSCAP toolset. In that post we learned how to run a basic scan via the scap-workbench in a desktop environment.

This post will focus on the Content, Profiles, and Targets.

Content

All content will be installed in the directory shown below.  The content in this directory will vary based on the installed OS (the content on my Fedora differs from RHEL for example).

/usr/share/xml/scap/ssg/content

The screenshot below contains a list of content installed by default on RHEL 7.

Screenshot from 2019-07-24 15-58-04.png

Additional content can be obtained and added to the content directory shown above.  For example, NIST content can be downloaded directly from the NIST website. Link below.

National Checklist Program Repository

In the screenshot below we have performed a search for all content that targets RHEL 7.6

Screenshot from 2019-07-25 11-45-44.png

 

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OpenSCAP Part 1: Introduction and Basic Usage for RHEL 7/CentOS 7/Fedora

openscap-base

Introduction

OpenSCAP is a standardized compliance solution for Linux. It is comprised of policies (NIST, STIG, etc) and tooling (oscap, scap-workbench) that allow you to scan and evaluate Linux hosts in order to validate their compliance with industry defined standards.

In addition to providing industry standard compliance rules, OpenSCAP also allows administrators to create custom compliance standards using the scap-workbench.

Administrators can then generate remediation files in bash, ansible or puppet.

Let’s get familiar with OpenSCAP below.

Getting Started

Below is an overview of the “Getting Started” workflow. In this workflow we are gonna run through a very simple use-case, scanning your local Fedora workstation.

  1. Install
  2. Choose Policy
  3. Modify/Adjust
  4. Scan
  5. Remediate

In the sections below we will walk through each of these steps in detail.

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RHEL 7 Two-Factor SSH Via Google Authenticator

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In this post,  I am going to walk you through the process of installing and configuring two- factor SSH authentication via Google Authenticator. My base system is running a fresh install of RHEL 7.2

Installation Steps

The first step on my system was to install autoreconf, automake, and libtool. These packages are required by the bootstrap.sh script that we will need to in a couple more steps.

# yum -y install autoconf automake libtool

Now, we are going to install Git.

#yum -y install git

One more dependency to knock out. Install pam-devel as shown below.

# yum -y install pam-devel

Next, we clone the google-authenticator Git repo. In this example, I am cloning to /root

# git clone https://github.com/google/google-authenticator.git
Cloning into ‘google-authenticator’…
remote: Counting objects: 1435, done.
remote: Total 1435 (delta 0), reused 0 (delta 0), pack-reused 1435
Receiving objects: 100% (1435/1435), 2.32 MiB | 0 bytes/s, done.
Resolving deltas: 100% (758/758), done.

Now change directory as shown below and run bootstrap.sh.

# cd /root/google-authenticator/libpam

# ./bootstrap.sh

Now run the following commands to finalize the module installs.

# ./configure

#make

#make install

Assuming that you do not run into any errors, the following modules will be installed.

  • /usr/local/lib/security/pam_google_authenticator.so
  • /usr/local/lib/security/pam_google_authenticator.la

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RHEL6: Cool PAM Tricks – Logging Terminal Keystokes

Pam-original-cooking-spray-72450This is a neat and very useful trick that I learned today. Lets say that you want to be able to monitor and log all keystrokes that are typed as root. This is particularly useful as normally you can only log when a user uses sudo to run a command. If the user has the abilty to become root however,  then they have effectively eluded yourattempts to track their activity. Like Thomas Magnum shaking a tail, they are free to scoot around your island with the top down.

So how do you stop this from occuring? How to you log all activity and keystrokes made by root without implementing a bloated 3rd party software that will probably cost and arm and a leg? You use PAM you dingbat.
 

The secret sauce in this security burrito is the pam_tty_audit.so module. Here is how to use it,

Below is my stock /etc/pam.d/system-auth file

#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_fprintd.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so md5 shadow nullok try_first_pass use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

Now look above and then look below at my modified system-auth file. Note the additonal session entry for pam_tty_audit.so.

[root@ip-172-31-21-28 pam.d]# cat system-auth
#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_fprintd.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so md5 shadow nullok try_first_pass use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_tty_audit.so enable=root
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

Note that you will need to add the pam_tty_audit.so call to your /etc/pam.d/password-auth as well to ensure that you capture all of root's keystrokes, no matter how they log in.

 

Related articles

Much Todo About Linux/RHEL Passwords
RHEL6 – How to Manually Logout of an Iscsi Disk
Fun With PAM: Working with pam_cracklib and pam_tally2

RHEL6: Composing Custom Auditd Rules for Fun and Profit

297247-typewriterAuditd gives you the ability to write your own custom audit rules. This functionality allows an administrator to keep a close eye on system calls, file access, and user behavior. This added functionality is especially useful in environments that are requred to adhear to compliance standards that are above and beyond normal standards. Think PCI.

Once of the simplest rules to add is a watch rule which can be set on files and directories. In the example below we are watching the /etc/passwd file for permission changes (writes and attibute changes specifically). We are creating a custom key to use for organizational purposes.

[root@ip-172-31-21-28 ~]# auditctl -w /etc/passwd -p wa -k edit_watch

Here is a cool one – lets audit all binary executions under /usr/bin.

[root@ip-172-31-21-28 ~]# auditctl -w /usr/bin -p x

Using the -l option you can list your current audit rules, and using the -s option you can see the current status of the auditd subsystem

[root@ip-172-31-21-28 ~]# auditctl -l
LIST_RULES: exit,always watch=/etc/passwd perm=wa key=edit_watch
LIST_RULES: exit,always dir=/usr/bin (0x8) perm=x

[root@ip-172-31-21-28 ~]# auditctl -s
AUDIT_STATUS: enabled=1 flag=1 pid=741 rate_limit=0 backlog_limit=320 lost=0 backlog=0

Want to get down and dirty with audit rules – you can check out the audit rules man page by running the command below.

[root@ip-172-31-21-28 ~]# man audit.rules

 

 

 

Related articles

RHEL6 – SELinux Troubleshooting II: Electric Boogaloo
Linux audit files to see who made changes to a file
A Brief Introduction to auditd

RHEL6: All Up in Your Face with Auditd

Strongbad2kqAuditd is the userland piece of the RHEL audit tool suite. When its up and running, audit messages sent by the kenel will be send to log files that you have configured. By default, only a small and limited number of messages will be picked up by Auditd; these are mostly messages related to authentication and authorization.

Auditd has three main config files as shown below

  • /etc/sysconfig/auditd – basic configuration options
  • /etc/audit/auditd.conf – main config file
  • /etc/audit/audit.rules – auditing rules

Auditd and Syslog:

Its possible to send audit messages to a syslog. By setting active=yes in /etc/audisp/plugins.d/syslog.conf you can send all your audit messages to syslog. If your system is setup to log to a remote syslog server, then your audit messages will go along for the ride as well. Note that you can also send audit messages to a remote logging server via native audit protocol over TCP. I am not going to go into this option, but I want to make sure that we are aware that it exists.

 

Looking for Audit Events in All the Wrong Places:

Auditd includes a handy-dandy tool for searching audit logs. Ausearch. You can check out all your current audit log messages using the command below.

[root@ip-172-31-21-28 ~]# ausearch -l

Viewing audit logs in their raw format can be accomplished with the command below

[root@ip-172-31-21-28 ~]# ausearch –raw

The -a option allows you to search by audit event ids

[root@ip-172-31-21-28 ~]# ausearch -a 282

Auditd also includes ausearch, which allows you to get a quick summary of audit events, rather than trying to view massive audit logs. Usage and output shown below.

root@ip-172-31-21-28 ~]# aureport

Summary Report
======================
Range of time in logs: 07/17/2014 10:21:36.438 – 07/17/2014 19:52:49.556
Selected time for report: 07/17/2014 10:21:36 – 07/17/2014 19:52:49.556
Number of changes in configuration: 4
Number of changes to accounts, groups, or roles: 24
Number of logins: 20
Number of failed logins: 4
Number of authentications: 75
Number of failed authentications: 3
Number of users: 3
Number of terminals: 18
Number of host names: 19
Number of executables: 14
Number of files: 0
Number of AVC's: 10
Number of MAC events: 20
Number of failed syscalls: 10
Number of anomaly events: 0
Number of responses to anomaly events: 0
Number of crypto events: 244
Number of keys: 0
Number of process IDs: 203
Number of events: 1132

You can also use aureport and ausearch together. Simliar to the powerfull partnership between Batman and Robin, these two tools complement each other in ways that you can only imagine. Check out my sexy bits below.

[root@ip-172-31-21-28 ~]# ausearch –start today –raw | aureport

Summary Report
======================
Range of time in logs: 07/17/2014 10:21:36.438 – 07/17/2014 20:01:01.911
Selected time for report: 07/17/2014 10:21:36 – 07/17/2014 20:01:01.911
Number of changes in configuration: 4
Number of changes to accounts, groups, or roles: 24
Number of logins: 20
Number of failed logins: 4
Number of authentications: 75
Number of failed authentications: 3
Number of users: 3
Number of terminals: 18
Number of host names: 19
Number of executables: 14
Number of files: 0
Number of AVC's: 10
Number of MAC events: 20
Number of failed syscalls: 10
Number of anomaly events: 0
Number of responses to anomaly events: 0
Number of crypto events: 244
Number of keys: 0
Number of process IDs: 205
Number of events: 1144

Want to know another cool tool that is part of auditd? I know, its a lot to take in at one time, but I am sure that you can handle it. Using autrace you can trace and investigate system calls made by a process. 

Want to see everything that nslookup is doing? Then run the command below.

[root@ip-172-31-21-28 ~]# autrace /usr/bin/nslookup google.com

This will output a pid for you to trace with ausearch.

Trace complete. You can locate the records with 'ausearch -i -p 3359'

 

Related articles

RHEL6- Getting Up Close and Personal With Rsyslog
Linux audit files to see who made changes to a file