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Managing and monitoring security updates

Red Hat Enterprise Linux 9

Update RHEL 9 system security to prevent attackers from exploiting known flaws

Red Hat Customer Content Services

Abstract

Learn how to install security updates and display additional details about the updates to keep your Red Hat Enterprise Linux systems secured against newly discovered threats and vulnerabilities.

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Chapter 1. Identifying security updates
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Keeping enterprise systems secure from current and future threats requires regular security updates. Red Hat Product Security provides the guidance you need to confidently deploy and maintain enterprise solutions.

1.1. What are security advisories?
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Red Hat Security Advisories (RHSA) document the information about security flaws being fixed in Red Hat products and services.

Each RHSA includes the following information:

  • Severity
  • Type and status
  • Affected products
  • Summary of fixed issues
  • Links to the tickets about the problem. Note that not all tickets are public.
  • Common Vulnerabilities and Exposures (CVE) numbers and links with additional details, such as attack complexity.

Red Hat Customer Portal provides a list of Red Hat Security Advisories published by Red Hat. You can display details of a specific advisory by navigating to the advisory’s ID from the list of Red Hat Security Advisories.

Figure 1.1. List of security advisories

Customer Portal: List of security advisories
View larger image
Customer Portal: List of security advisories

Optionally, you can also filter the results by specific product, variant, version, and architecture. For example, to display only advisories for Red Hat Enterprise Linux 9, you can set the following filters:

  • Product: Red Hat Enterprise Linux
  • Variant: All Variants
  • Version: 9
  • Optionally, select a minor version.

You can list all available security updates for your system by using the dnf utility.

Prerequisites

  • A Red Hat subscription is attached to the host.

Procedure

  • List all available security updates which have not been installed on the host: 

    # dnf updateinfo list updates security
…
RHSA-2019:0997 Important/Sec. platform-python-3.6.8-2.el8_0.x86_64
RHSA-2019:0997 Important/Sec. python3-libs-3.6.8-2.el8_0.x86_64
RHSA-2019:0990 Moderate/Sec.  systemd-239-13.el8_0.3.x86_64
…
    Copy to Clipboard Toggle word wrap

You can list installed security updates for your system by using the dnf utility.

Procedure

  • List all security updates which are installed on the host: 

    # dnf updateinfo list security --installed
…
RHSA-2019:1234 Important/Sec. libssh2-1.8.0-7.module+el8+2833+c7d6d092
RHSA-2019:4567 Important/Sec. python3-libs-3.6.7.1.el8.x86_64
RHSA-2019:8901 Important/Sec. python3-libs-3.6.8-1.el8.x86_64
…
    Copy to Clipboard Toggle word wrap

    If multiple updates of a single package are installed, dnf lists all advisories for the package. In the previous example, two security updates for the python3-libs package have been installed since the system installation.

You can use the dnf utility to display a specific advisory information that is available for an update.

Prerequisites

  • A Red Hat subscription is attached to the host.
  • You know the ID of the security advisory.
  • The update provided by the advisory is not installed.

Procedure

  • Display a specific advisory, for example: 

    # dnf updateinfo info RHSA-2019:0997
====================================================================
  Important: python3 security update
====================================================================
  Update ID: RHSA-2019:0997
       Type: security
    Updated: 2019-05-07 05:41:52
       Bugs: 1688543 - CVE-2019-9636 python: Information Disclosure due to urlsplit improper NFKC normalization
       CVEs: CVE-2019-9636
Description: …
    Copy to Clipboard Toggle word wrap

Chapter 2. Installing security updates
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In RHEL, you can install a specific security advisory and all available security updates. You can also configure the system to download and install security updates automatically.

2.1. Installing all available security updates
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To keep the security of your system up to date, you can install all currently available security updates using the dnf utility.

Prerequisites

  • A Red Hat subscription is attached to the host.

Procedure

  1. Install security updates using dnf utility: 

    # dnf update --security
    Copy to Clipboard Toggle word wrap

    Without the --security parameter, dnf update installs all updates, including bug fixes and enhancements.

  2. Confirm and start the installation by pressing y: 

    …
Transaction Summary
===========================================
Upgrade  … Packages

Total download size: … M
Is this ok [y/d/N]: y
    Copy to Clipboard Toggle word wrap

  3. Optional: List processes that require a manual restart of the system after installing the updated packages: 

    # dnf needs-restarting
1107 : /usr/sbin/rsyslogd -n
1199 : -bash
    Copy to Clipboard Toggle word wrap

    The previous command lists only processes that require a restart, and not services. That is, you cannot restart processes listed using the systemctl utility. For example, the bash process in the output is terminated when the user that owns this process logs out.

In certain situations, you might want to install only specific updates. For example, if a specific service can be updated without scheduling a downtime, you can install security updates for only this service, and install the remaining security updates later.

Prerequisites

Procedure

  1. Install a specific advisory, for example: 

    # dnf update --advisory=RHSA-2019:0997
    Copy to Clipboard Toggle word wrap

  2. Alternatively, update to apply a specific advisory with a minimal version change by using the dnf upgrade-minimal command, for example: 

    # dnf upgrade-minimal --advisory=RHSA-2019:0997
    Copy to Clipboard Toggle word wrap

  3. Confirm and start the installation by pressing y: 

    …
Transaction Summary
===========================================
Upgrade  … Packages

Total download size: … M
Is this ok [y/d/N]: y
    Copy to Clipboard Toggle word wrap

  4. Optional: List the processes that require a manual restart of the system after installing the updated packages: 

    # dnf needs-restarting
1107 : /usr/sbin/rsyslogd -n
1199 : -bash
    Copy to Clipboard Toggle word wrap

    The previous command lists only processes that require a restart, and not services. This means that you cannot restart all processes listed by using the systemctl utility. For example, the bash process in the output is terminated when the user that owns this process logs out.

2.3. Installing security updates automatically
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You can configure your system so that it automatically downloads and installs all security updates.

Prerequisites

  • A Red Hat subscription is attached to the host.
  • The dnf-automatic package is installed.

Procedure

  1. In the /etc/dnf/automatic.conf file, in the [commands] section, make sure the upgrade_type option is set to either default or security: 

    [commands]
#  What kind of upgrade to perform:
# default                            = all available upgrades
# security                           = only the security upgrades
upgrade_type = security
    Copy to Clipboard Toggle word wrap

  2. Enable and start the systemd timer unit: 

    # systemctl enable --now dnf-automatic-install.timer
    Copy to Clipboard Toggle word wrap

Verification

  1. Verify that the timer is enabled: 

    # systemctl status dnf-automatic-install.timer
    Copy to Clipboard Toggle word wrap

Legal Notice
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The text of and illustrations in this document are licensed by Red Hat under a Creative Commons Attribution–Share Alike 3.0 Unported license ("CC-BY-SA"). An explanation of CC-BY-SA is available at http://creativecommons.org/licenses/by-sa/3.0/. In accordance with CC-BY-SA, if you distribute this document or an adaptation of it, you must provide the URL for the original version.
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