Ubuntu Wiki

Standard Support

• What does standard security support mean?

  • Canonical employees working on the Ubuntu Security Team provide security updates for supported software in the Ubuntu distribution. Security updates are in part prioritized based on severity of impact, exploitability and number of affected users.

  • Previously referred to as "Official Support"
• What software is supported by the Ubuntu Security team?

  • Ubuntu is currently divided into four components: main, restricted, universe and multiverse. All binary packages in main and restricted are supported by the Ubuntu Security team for the life of an Ubuntu release, while binary packages in universe and multiverse are supported by the Ubuntu community.

• Who can receive standard support?

  • Standard Support is provided free of charge to all users of Ubuntu during the life of an Ubuntu release.

• How do seeds impact standard support?

  • Seeds determine in which component a package resides. All binary packages in the main and restricted components receive support for the life of an Ubuntu release.

  • The Supported field in the Packages file for the main and restricted components may be inaccurate, especially in the case of non-LTS releases. Today, all releases have unified support lengths.

• What is extended support?

  • Ubuntu Pro customers may receive additional security support beyond what is freely available via standard support.

  • ESM customers (ESM is included in Ubuntu Pro) can receive security updates for high and critical CVEs (common vulnerabilities and exposures) for the the entire collection of software packages shipped with Ubuntu, including the Ubuntu Universe repository, for 10 years.

  • A FAQ specifically about the security patches included in Ubuntu Pro is available here.

• How will support for Ubuntu Touch be provided?
  • As of 2017/06/15, Ubuntu Touch no longer receives security support.
• How will support for Ubuntu Core be provided?

  • Ubuntu Core 15 security updates will be provided via its PPA overlay only. Ubuntu Core 16 inherits security updates from Ubuntu 16.04. Ubuntu Core 16 snaps are automatically refreshed via the snap automated update mechanism.

Repositories and Updates

How are the "-updates" and "-security" pockets different?

TLDR;

• -updates includes things that have gone through the StableReleaseUpdates process, and contain various important bug fixes. Anything built for "-updates" is built on top of which ever version of a package is newest between "-updates" and "-security", so that nothing in "-updates" will introduce security regressions.

• -security includes only updated packages that contain security-related fixes, and are built to not require anything from "-updates". Anything built for "-security" is built on top of which ever version of a package is newest between "-updates" and "-security", so that nothing in "-security" will introduce bug regressions.

When the security team prepares updates for the "-security" pocket they take whichever is the highest version from either the "-updates" OR the "-security" pocket and then patch that and release it to the "-security" pocket. As such, "-security" can end up containing some changes from "-updates". This is due to the nature of package versioning and to ensure that for all users (regardless of whether they have only "-security" or both "-security" + "-updates" enabled) that they can always upgrade to the security updated version (ie. the version number has to be strictly greater than anything prior to that from both "-updates" and "-security").

When doing security updates, any required dependencies that are not already in the "-security" pocket are also copied over from the "-updates" pocket as needed.

How are components and pockets used in the builds, and how do they affect security updates?

When packages are built, only certain components are available during the build:

• main: built with only the main component enabled

• restricted: built with main and restricted components enabled

• universe: built with main and universe components enabled

• multiverse: built with main, restricted, universe and multiverse components enabled

Ubuntu also has several pockets that further divide the archive: release, security, updates, proposed and backports. The pocket can be found by looking at the Distribution entry of a source package. The release pocket is simply the name of the release, and the other pockets are denoted by <release name>-<pocket>. For example, the release pocket for Ubuntu 16.04 LTS, the Xenial Xerus, is simply xenial, while the security pocket for Ubuntu 16.04 LTS is xenial-security. Packages in release, security and updates are supported by the Ubuntu Security team, while packages in backports are supported by the community and packages in proposed are the responsibility of the uploader. When packages are built, only certain pockets are available during the build:

• release: during the development cycle, this is the only pocket that is used. Once the development version is released, the release pocket is frozen and does not change.

• security: built with release and security. UpdateProcedures gives the process used for creating security updates.

• proposed: built with release, security, updates and proposed

• updates: as a matter of Ubuntu policy, packages in updates are not directly built, but rather copied from proposed after they have been tested. See StableReleaseUpdates for details. If a special circumstance warrants building a package in updates without going through proposed first, it would be built with release, security and updates (also, the default configuration for unofficial PPAs is to build with this configuration).

• backports: built with release, security, updates and backports. See UbuntuBackports for details.

What repositories and pockets should I use to make sure my systems are up to date?

• By default, Ubuntu systems have both the security and updates pockets enabled. Systems configured to use only the security pocket are also supported. (This requires installing from the original release media, as the point release media contains packages from the updates pocket and will result in difficulties running with only the security pocket enabled.)

• While packages are copied from security to updates frequently, it is recommended that systems always have the security pocket enabled, and use security.ubuntu.com for this pocket. For all other pockets feel free to use archive.ubuntu.com or an archive mirror. This combination will ensure you are able to download important updates immediately while taking advantage of the mirror network or archive.ubuntu.com for all other downloads. Ubuntu systems are configured in this manner by default.

How do I automatically install security updates?

See https://help.ubuntu.com/community/AutomaticSecurityUpdates

There is a security update available that claims it is a "Fake sync from Debian" -- should I be concerned?

No. During the development cycle, source packages that have not been modified by Ubuntu developers are copied from Debian by Launchpad to Ubuntu automatically in a process referred to as "syncing". For some security updates that Debian publishes for its released versions, the Ubuntu Security Team will copy these updates to the corresponding Ubuntu release where the Ubuntu version does not differ from Debian. However, the same launchpad process is not used, as there are additional consistency checks and review the Ubuntu Security Team performs before copying, and the tool that is used to do this is called fake-sync, because it is intended to mimic Launchpad's "syncing" behavior. These "fake-synced" updates should only appear for packages in the universe and multiverse pockets.

When I run a virus scanner on my local Ubuntu Archive Mirror, it claims there are malware/trojans/viruses in it. What is going on?

Several packages in the Ubuntu Archive produce false positives since they contain examples of malware that do not pose a risk. Much of this has been discussed in Bug 592871.

• The Ubuntu Security Team maintains a list of known false positives.

Packages

• Where did mod_security go?

  • The license to mod_security did not allow for redistribution, so it was removed from Debian and Ubuntu after 6.06 (Dapper):

    • http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=313615

    • http://groups.google.com/group/linux.debian.legal/browse_thread/thread/d4b4a74c82042abd

  • The licensing issue has been resolved and mod_security is back in the archive as of Ubuntu 9.04 (Jaunty):

    • https://bugs.launchpad.net/ubuntu/+source/libapache-mod-security/+bug/247268

Versions

Ubuntu, like most other Linux distros, releases security updates by patching specific issues rather than updating whole versions of software. This is to keep the packages in a stable release as close to their original version as possible to avoid introducing unintended regressions. For more details, see Stable Release Updates.

Sometimes external security vendors doing software version scanning against Ubuntu systems do not check actual package versions, leading to false positives in their scan reports. For an authoritative source of what packages may have outstanding vulnerabilities, the Ubuntu CVE Tracker can be consulted.

• Due to various difficulties in the ability to backport specific security patches, there are certain packages that are typically excluded from this policy and get full-version upgrades:
  • OpenJDK
  • MySQL
  • MariaDB
  • PostgreSQL
  • ClamAV
  • Chromium
  • Firefox
  • Thunderbird
  • WebKitGTK
  • ca-certificates
  • intel-microcode, amd-microcode
  • NVIDIA driver packages

Architectures

Ubuntu is built for many architectures. Ubuntu officially supports i386⁵, amd64, armhf, arm64, ppc64el, s390x, and riscv64. Packages for i386 and amd64 are hosted on http://archive.ubuntu.com/ubuntu/dists/<release>/ and packages for all other architectures are hosted on http://ports.ubuntu.com/dists/<release>/.

1. armhf is ARMv7

2. Release has reached end of standard security support. Extended support may be purchased for 14.04 LTS, 16.04 LTS, 18.04 LTS and 20.04 LTS.

3. While the architecture is listed in ports.ubuntu.com for this release, it should be considered a supported architecture
4. Architecture is supported for 18 months on this LTS release
5. Only a limited set of packages is supported for i386 on Ubuntu 19.10 onwards

6. 22.04 and newer drop support for Power8 and require Power9 or newer

7. Release has reached end of life.

Endianness

Sometimes a security vulnerability affects a particular architecture or endianness. When an issue affects only a single architecture or endianness, we will try to indicate this in our CVE tracker. Most issues affect all architectures. Most architectures in Ubuntu are little-endian, some are so-called bi-endian and some big-endian. In Ubuntu, the endianness of a particular architecture can be see in the following table:

Software

SSH

• When I run ssh HOST sudo CMD..., I can see the password as I type it. How do I fix that?

  • There is no "tty" allocated when running commands directly via ssh, please add the "-t" flag.

• When I connect to my ssh server port, I can see a banner with the exact version I'm running. Can we include a patch to disable the version number?

  • There is an upstream bug that gets into detail about this feature, but Ubuntu does not want to carry the patches unless upstream approves.

  • Hiding the version number is Security through obscurity, which is not real security.

  • SSH clients, including OpenSSH, usually parse the version string in order to identify known bugs/features with a particular version of the server. Changing the values could introduce communication problems with certain clients. See compat.c in the OpenSSH source code.

Sudo

• Why does Ubuntu disable the root account and use sudo instead?

  • See RootSudo for a thorough discussion, but simply put, sudo offers many benefits including (but not limited to):

    • protecting the user from accidentally damaging parts of the system
    • providing a log audit trail
    • preventing brute-force login and ssh attacks to a well known account
    • authentication timeouts
    • fine-grained granting of privileges
• I am not prompted for my password when I run "sudo" for a second time!

  • sudo is designed to keep a "ticket" valid for 15 minutes after you use your password the first time. This is configurable. Please read man sudoers:

    timestamp_timeout
        Number of minutes that can elapse before sudo will ask
        for a passwd again.  The default is 15.  Set this to 0
        to always prompt for a password.  If set to a value
        less than 0 the user’s timestamp will never expire.
        This can be used to allow users to create or delete
        their own timestamps via sudo -v and sudo -k respec‐
        tively.

• If sudo authentication does not immediately expire, doesn't that allow for privilege escalation for malware and local users?
  • Giving untrusted users access to your account or running untrusted code can allow privilege escalation via sudo, but Ubuntu does not (and by default cannot) provide protections against users running code as themselves. Some protections against these sort of attacks are:
    • do not open files or run/install programs from untrusted sources
    • enable locking of your screensaver
    • using 'sudo -k' or 'sudo -K' to remove the timestamps (see 'man sudo' for details).

    • add the above 'sudo -k' to ${HOME}/.bash_logout to automatically expire timestamps when the associated shell exits. However, note that this will only work for shells that are started as login shells; gnome-terminal by default does not start shells this way. Either edit the profile configuration through the gui or run the following command to configure gnome-terminal to start shells as login shells:

      for dir in $(gconftool-2 --all-dirs /apps/gnome-terminal/profiles) ; do
          if [ "$(gconftool-2 -g ${dir}/login_shell 2> /dev/null)" = "false" ] ; then 
              gconftool-2 -s -t bool ${dir}/login_shell true
          fi
      done

      Different shells and terminals may have different behaviors, see their manpages for more details.
    • adjusting timestamp_timeout in /etc/sudoers (using visudo) (see above, and 'man sudoers' for details)
    • using a virus scanner such as clamav on your files

    • protecting specific applications with Apparmor or SELinux

Rescue Mode

• I am not prompted for a password when going into rescue mode!
  • This is related to 'sudo', above. Because in Ubuntu there is no root password, there is nothing to prompt for. In general, not prompting for a password in single user mode does not decrease security because it requires physical access to the machine. An attacker with physical access can bypass this restriction easily (eg with bootable media or removing the hard drive). If you decide to set a root password, you will be prompted for it in rescue mode. (This still won't protect against bootable media or removing the hard drive. To protect against these, select Full Disk Encryption when installing Ubuntu.)

UFW

• Why is the ufw firewall not enabled by default?

  • ufw is available in all new installations of Ubuntu since 8.04 LTS, but is disabled by default. The standard Ubuntu installation has a no open service ports policy, so enabling the firewall by default doesn't gain any extra security in the default installation, but could provide confusion for people new to Ubuntu when new software that is installed does not work because of restrictive firewall rules. As a result, when first adding ufw to Ubuntu it was decided that users must 'opt-in' to using the firewall. In Ubuntu 9.04 and later, you can enable ufw during installation using preseeding. See /usr/share/doc/ufw/README.Debian for details.

GNOME Display Manager (gdm)

• How do I disable the face browser at the login screen?

  • gdm 2.28, as included in Ubuntu 9.10 and later, has been rewritten and does not have the gdmsetup graphical configuration tool the previous versions had. gdm now stores its settings using GConf. To disable the face browser, use the following command: sudo -u gdm gconftool-2 --set --type boolean /apps/gdm/simple-greeter/disable_user_list true

  • Here are some links with more information:

    • Ubuntu bug ("No GUI option to disable face browser")

    • Upstream bug ("There's no simple way to disable the face browser")

    • Upstream bug to re-implement `gdmsetup` ("GDM rewrite needs a configuration GUI panel similar to 2.20 (gdmsetup)")

gnome-keyring

Q: Does using gnome-keyring weaken security?

A: For most users in typical environments, no. Proper use of gnome-keyring should increase security by encouraging users to store passwords securely in the keyring rather than resorting to other less secure means of storing their passwords (eg, sticky notes on the monitor or a plain text file somewhere on disk).

Basically, gnome-keyring can store passwords for you (by integrating with SecretService on modern releases of Ubuntu). The passwords are stored in encrypted keyrings that are not available to applications until the keyring is unlocked. A common keyring is the 'login' keyring, but others can be used. Once the keyring is unlocked, applications can ask gnome-keyring for passwords and use them so that users don't have to remember them all, or be hassled with password prompts all the time. A keyring can be locked after it is unlocked. Because gnome-keyring uses protected memory, other users on the system cannot access the keys within a user's keyring (see man mmap and man mlock).

Gnome/Ubuntu integration does a few things (see the upstream documentation for more details):

• The 'login' keyring is configured, via PAM, to be automatically unlocked upon successful authentication via PAM (ie, when you login)
• All keyrings are locked on logout of the user's session

This provides:

• A good usability experience
• Protection against access from anyone to keys when the user is not authenticated
• Protection against other users on the system at all times

Some people may not like to use keyrings in general and there are certain environments where their use is not appropriate. Users can always choose to not store their passwords in the keyring at all. Furthermore, gnome-keyring behavior can be adjusted:

• Temporarily by using seahorse and manually locking the unlocked keyring

• Permanently by changing the passphrase of the 'login' keyring
• Permanently by removing gnome-keyring from the PAM stack

Please note that by changing this behavior, programs that need access to the unlocked passwords will prompt you for the keyring passphrase whenever they need it.

In general, using a keyring does not weaken the security of the system. To use them safely^2,3:

• You should choose a strong login passphrase (eg, using a mixture of letters, numbers, capitalization and non-alphanumerics that is at least 8 (preferably 12 or more) characters long and not subject to a dictionary attack). This login passphrase should be memorized, and not written down.
• You should always lock your screen when you step away from your system. You can set a short inactivity timeout and/or better yet, use 'ctrl+alt+l' or activate the screensaver from within your session every time you step away.
• Do not use shared login accounts

Notice that these recommendations are no different from when you are not using a keyring (ie, you always want a strong login passphrase, to lock your screen, and never share your login account).

[1] While the upstream documentation implied keyrings may be locked at various times when the computer is locked (as of 2020/02/26, "Hunkering down and discarding all secrets when your computer is locked"), keyrings are not locked/unlocked on screenlock/screenunlock since programs in the user's session may require access to the keyring during screenlock (eg, an email client). It is possible to configure gnome-keyring to lock/unlock the keyring when going into/coming out of suspend and/or hibernate.

[2] If you leave your computer powered on in an environment where it might be stolen (eg, a hotel room), software techniques cannot protect you. In general, in these environments the computer should be completely powered off and use disk encryption. Disk encryption as well as discussion to mitigate hardware, firmware, BIOS, cold-boot or 'evil maid' attacks are beyond the scope of this FAQ.

[3] gnome-keyring FAQ

Firefox AppArmor profile

• Why is the profile disabled by default?

  • Starting with Ubuntu 9.10, firefox ships an AppArmor profile. It is known to work well in the default Ubuntu installation with extensions, plugins and helper applications provided in the Ubuntu archive. Firefox, like all browsers, is a very complex piece of software that can do much more than simply surf web pages. As such, enabling the profile in the default install could affect the overall usability of Firefox in Ubuntu, which could end up decreasing the security of the overall system. Users who know nothing about AppArmor who encounter AppArmor denials might turn off AppArmor entirely, losing the protections afforded by the existing profiles. Enabling the profile for all users must be very carefully considered.

• Could the user be prompted on upgrade to enable the profile?

  • Asking the user on upgrade or installation is not a valid option for Ubuntu, because the question could be confusing and boils down to "do you want better security?" People will almost always answer "yes", which is essentially the same as enabling the profile by default. Adding a low priority debconf question which can be preseeded might be implemented in a future release.

• Will the profile be enabled by default in a future release of Ubuntu?

  • Possibly. As mentioned, Firefox is a very complex application on its own, and when you consider third-party plugins, extensions, helper applications and Ubuntu derivatives, it becomes very difficult to ensure that the profile provides the proper level of usability and confinement. It is known to work well in the default Ubuntu installation with extensions, plugins and helper applications provided in the Ubuntu archive. If the profile can be shown to work for the vast majority of users in Ubuntu and its derivatives, and AppArmor user-space tools mature to the point that they are usable by regular users, enabling the profile by default can be considered.

• What does the profile protect against?
  • The goals of the profile are to provide a good usability experience with strong additional protection. The profile allows for the use of plugins and extensions, various helper applications, and access to files in the user's HOME directory, removable media and network filesystems. The profile prevents execution of arbitrary code, malware, reading and writing to sensitive files such as ssh and gpg keys, and writing to files in the user's default PATH. It also prevents reading of system and kernel files. All of this provides a level of protection far exceeding that of normal UNIX permissions.

  • In Ubuntu 10.10 the default shipped profile is the same as above, but its use of includes allows for much greater flexibility for tightly confining firefox. /etc/apparmor.d/usr.bin.firefox is a very restricted profile, but includes both /etc/apparmor.d/local/usr.bin.firefox and /etc/apparmor.d/abstractions/ubuntu-browsers.d/firefox. /etc/apparmor.d/abstractions/ubuntu-browsers.d/firefox contains other include files for tasks such as multimedia, productivity, etc and the file can be manipulated via the aa-update-browser command. /etc/apparmor.d/local/usr.bin.firefox is used for site-specific adjustments (see /etc/apparmor.d/local/README for details and caveats). A future release of Ubuntu may allow debconf configuration for /etc/apparmor.d/abstractions/ubuntu-browsers.d/firefox to allow preseeding.

• How do I enable or disable the profile?

  • The profile can be enabled by using sudo aa-enforce /etc/apparmor.d/usr.bin.firefox (use /etc/apparmor.d/firefox-3.5 in Ubuntu 9.10). The profile can be temporarily disabled by performing sudo apparmor_parser -R /etc/apparmor.d/usr.bin.firefox and permanently disabled with sudo apparmor_parser -R /etc/apparmor.d/usr.bin.firefox ; sudo ln -s /etc/apparmor.d/usr.bin.firefox /etc/apparmor.d/disable/usr.bin.firefox. See the Ubuntu AppArmor documentation for more details on using AppArmor.

• The profile doesn't work for me, what should I do?

  • See DebuggingApparmor for how to diagnose, report and fix bugs in AppArmor profiles. You may also disable the profile (see above).

• Can I adjust the profile?

  • Certainly! You can add additional access rules or remove rules in the profile for your requirements. For firefox, simply adjust the profile /etc/apparmor.d/usr.bin.firefox and reload it with sudo apparmor_parser -r -T -W /etc/apparmor.d/usr.bin.firefox. See the Ubuntu AppArmor documentation for more details on using AppArmor. If you feel your additions would benefit all Ubuntu users, please consult DebuggingApparmor and file a bug. Keep in mind /etc/apparmor.d/usr.bin.firefox is a Debian conffile, which means on certain package upgrades, you will be prompted for what to do with the changes. In Ubuntu 10.10 you can fine-tune the profile using the aforementioned ubuntu-browsers.d abstraction mechanism and also adjust /etc/apparmor.d/local/usr.bin.firefox and avoid being prompted on upgrade.

Update Manager doesn't prompt for security updates

• Why does update-manager no longer prompt for the user's password?

  • As of Ubuntu 11.10, update-manager no longer prompts for the user's password to apply updates. This was decided to improve usability and to make it easier for users to apply security updates and therefore increase system security. The rationale is as follows:

    • Like in previous releases, by default only people in the admin group are allowed access to perform security updates.

    • Only updates for already installed software can be applied without a password. Installing additional software still requires people to enter their password.
    • The password prompt had become an irritant for some people such that they would just press 'Cancel' instead of installing the updates. The password prompt decreased system security for those users.

    • People that did dutifully apply updates became conditioned to enter their privileged password perhaps daily. When the user is prompted for the password, it should mean something and the frequency of update-manager updates meant that some people no longer thought about why they were entering their password. For these users, the password prompt had the potential to reduce security.

    For environments where this change is deemed not appropriate, this functionality can be disabled by the administrator via PolicyKit or by creating users that are not in the admin group (a recommended practice to begin with).

NetworkManager system connections

• Why does NetworkManager now store its connection information in /etc?

  • As of Ubuntu 11.10, NetworkManager defaults to having connections "Available to all users" which stores connection information in /etc/NetworkManager/system-connections. Files in this directory are set so that only the root user is able to read them. If you prefer your connection information to be stored in your keyring, uncheck "Available to all users" in NetworkManager for this connection.

SHA512-crypt as default

• Why does Ubuntu use the SHA512-crypt key derivation function by default when storing passwords?

  • Starting with Ubuntu 8.10, Ubuntu moved from the old (and now untrusted) MD5-crypt key derivation function in glibc crypt() to the SHA512-crypt glibc crypt() key derivation function (hereafter known as SHA512-crypt) with an 8 character salt and default 5000 rounds (adjustable) to increase CPU requirements (aka, key stretching. Note, PBKDF1 and PBKDF2 are NIST approved methods to apply key-stretching by using key derivation functions). A requirement for glibc was to use a standards-based algorithm and since the SHA512 hash algorithm is recommended by NIST, it is suitable for use in applications with US-based requirements and thus added to glibc.

    Other algorithms exist however. Bcrypt is based on the blowfish cipher and was designed to be computationally expensive (being computationally expensive is desirable in a password hashing algorithm because it helps slow down brute-force attacks since an attacker can make fewer guesses per second). Like SHA512-crypt, bcrypt is adaptable by having an adjustable cost (similar to the adjustable rounds in SHA512-crypt). Bcrypt is often cited as a better choice than SHA512-crypt (indeed OpenSUSE uses bcrypt by default) because it is slower to compute on CPUs and GPUs. It is not meaningfully slower in certain other situations however, which has led to the creation of scrypt. Neither bcrypt nor scrypt have received review by NIST, and are therefore not on their recommended list.

    Which is best? This is subjective-- scrypt is more computationally expensive than bcrypt, but is too new to recommend. bcrypt is more computationally expensive than SHA512-crypt, but is not on the NIST recommended list. SHA512-crypt with its 5000 rounds of key-stretching and widespread review of its hashing algorithm is standards-approved, is considered good enough for the foreseeable future and is considered a safe default. Ubuntu will continue to monitor other algorithms such as scrypt or a new SHA-3-based key derivation function and move away from SHA512-crypt when a more appropriate alternative is available (note: there is currently no reason to migrate away from SHA-2 to SHA-3).

curl

• curl in Ubuntu 14.04 LTS and newer drops support for weak ciphers, including rc4, 64 bit ciphers, 56 bit export ciphers, and 40 bit export ciphers. If the server cannot be upgraded to support modern cipher suites, the --ciphers command line option can be used to connect using weak ciphers: curl --ciphers RC4-SHA:RC4-MD5 https://foo.example.com/

OpenSSL

• All supported versions of Ubuntu have been patched to prevent the "heartbleed" bug (CVE-2014-0160). Ubuntu 14.04 LTS did not receive a wholesale OpenSSL version update because 1.0.1g was provided very late in the Ubuntu 14.04 LTS development and testing schedule; backporting only the security fix to our 1.0.1f-1ubuntu2 packages allowed us to avoid a regression that was introduced in upstream OpenSSL 1.0.1g.

webkit

The following packages containing a webkit engine cannot currently be updated to fix security issues: webkitgtk, qtwebkit-source, qtwebkit-opensource-src, wpewebkit.

WebKitGTK

While attempts will be made to update to new upstream major versions when possible, new dependency requirements may prevent doing so. Currently, newer versions require a more recent version of GCC than is available in Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS.

mozjs

The GNOME desktop requires the SpiderMonkey javascript engine from Mozilla, which is packaged as mozjs38, mozjs52, mozjs68, mozjs78, mozjs91, etc, and interfaces with it via gjs. Mozilla does not provide separate security maintenance for the SpiderMonkey project and instead irregularly releases new versions which break backwards compatibility of JavaScript language features (used by gnome-shell, extensions, applications) and the C++ API (used by gjs). Fixes for vulnerabilities are not always marked and the project progresses at a rapid pace making it prohibitive to backport security fixes. Because of this, security support for mozjs is provided by providing new versions of mozjs as they become available.

grub, grub2, grub2-unsigned, grub2-signed

Sometimes people ask why we have chosen to ignore CVEs on the grub2 package. The grub packaging is very complicated. The grub2 source package is mostly used with BIOS / CSM mode booting, which has no security boundaries. Without any security boundaries, there's no point to calling any given bugs in the code as "security bugs". Any bugs that allow bypassing secure boot are eligible for security fixes, and those will happen in the grub2-signed and grub2-unsigned packages. (The split is an artifact of the build process; it is not necessary for users to understand why there are two source packages. In short, the unsigned variant is built first and then the signed variant packages those binaries after they are signed outside the build environment.)

binutils

The binutils package is a standard tool in compiling and maintaining software. The various binary execution formats are very intricate and involved. This makes binutils a very popular target of fuzzing enthusiasts, who generate malicious inputs to programs to identify where input validation is weak or missing entirely. This is all well and good, everybody benefits from more reliable software. However, the CVEs that are generated as part of this process are not relevant for the clear majority of users: most people just use these tools to compile source code to executable code. They have already decided that they trust the inputs and that they are going to execute the outputs. These vulnerabilities are only relevant for people who use binutils to perform binary analysis on untrusted inputs -- such as malware analysis -- and an unconfined binutils is not suitable for this task, as it was intended to be a useful tool for programmers, not security professionals. Tools such as Ghidra or IDA Pro would be better suited for malware analysis, ideally when run in a confined environment.

Because customers ask us for these fixes, we do occasionally release binutils security fixes where we believe that the risks of regression are low enough versus the very low security value of the fixes.

MySQL

Oracle does not provide details about the CVEs/vulnerabilities they publish for MySQL or the changes/patches needed to fix them. Because of this we currently do not patch MySQL and instead do full version upgrades when there is a new release upstream that addresses security issues.

Hardening Guide

The default installation of Ubuntu should make reasonable security / usability tradeoffs for most users. It is our goal that you can use Ubuntu without worrying about security and also not be artificially restricted in what you can do with your computer. However, these tradeoffs may not be ideal for all users. Some people may wish to subscribe to Ubuntu Pro in order to deploy industry-standard security benchmarks like FIPS or CIS benchmarks or DISA STIGs.

We've collected some suggestions for proactive hardening steps that system administrators can apply without committing fully to the more comprehensive security policies. We suggest considering:

• Disable SSH password authentication. Weak passwords are a leading cause of security breaches. It is far safer to use SSH keys or certificates for authentication to SSH servers.

• Disable pam_env.so user_readenv support in all PAM services. Allowing users to set environment variables inside the PAM stack is problematic.

• Raise the vm.mmap_rnd_compat_bits and mmap_rnd_bits settings. Ubuntu uses Address Space Layout Randomization to change some deterministic attacks into probabilistic attacks by randomizing the addresses uses for executables and libraries. Different architectures will have different allowed ranges and the defaults must be chosen in mind of the total amount of memory required by the process with the most stringent combination of alignment requirements and size requirements. Your workload may allow you to raise these values and increase the value of the probabilistic defense. Your workload may require larger contiguous chunks of memory than is available with defaults and require you to lower these values.

• Set BIOS "user" and "administrator" passwords, if available, to prevent disabling Secure Boot. Be careful -- recovering from lost BIOS passwords may be painful or impossible.
• Enable Full Disk Encryption during installation. Be careful -- recovering from a lost disk unlock password may be painful or impossible. You will need to enter a password during the Ubuntu startup process, so it is most applicable to laptops used for travel.
• Configure the screen-locker to lock the screen after a period of inactivity. While it is better to explicitly lock your desktop when walking away, the screen lock on idle time can help if you forget.

• Install and configure bolt to limit the functionality of Thunderbolt devices on your computer, which expose raw PCIe through a convenient port. Be careful -- this can prevent you from using your computer if not configured correctly.

• Install and configure usbauth or usbguard to limit the functionality of USB devices on your computer. Be careful -- this can prevent you from using your computer if not configured correctly.

• Install and configure a firewall. UFW is an easy front-end to help you get started if you don't already have a favorite.

• Set sysctl dev.tty.legacy_tiocsti if your kernel has it available to prevent the use of the TIOCSTI ioctl. This is probably safe -- there are very few legitimate uses of this ioctl in the world.

• List unused network protocols, drivers, line disciplines, via /etc/modprobe.d settings to prevent automatic kernel module loading these features.

Vulnerabilities

• What does CVE stand for?

  • Common Vulnerabilities and Exposures. From their FAQ:

    • CVE is a list of information security vulnerabilities and exposures that aims to provide common names for publicly known problems. The goal of CVE is to make it easier to share data across separate vulnerability capabilities (tools, repositories, and services) with this "common enumeration."