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Linux Antivirus? (lemmy.wtf)
submitted 11 months ago by to c/linux@lemmy.world
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I'm about to install bazzite on my wife's older (2017) Windows 10 machine, and I've been going over how to recreate everything she currently has. Most programs (even proprietary ones) are not an issue, but I'm not finding much in the antivirus department.

I never even thought to install one on my Linux machine (also on bazzite, but I have used other distros in the past). So although I am no stranger to Linux, this issue blindsided me.

I know clamav exists, and I'm educating myself on how to use it, but a GUI would be nice for the wife. She's not afraid of the terminal, but she likes the convenience of GUI programs.

Any suggestions? What do you use? Or is it just generally accepted that one should be careful and keep things up-to-date and that's enough?

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[–] 2 points 11 months ago (8 children)

AppImages have no sandboxing as you said. They also rely on the deprecated SUID-root binary FUSE2. AppImages are bad for security but they are convenient. A malicious AppImage could for example connect to org.freedesktop.secrets and access your keychain, or run a script that places a script called "sudo" in $HOME/.local/share/bin that is preferred over the real sudo and logs a password, or encrypt your files in a ransomware attack, or exfiltrate your session cookies from Firefox or Chromium browsers.

Flatpaks on the other hand are sandboxed. IIRC Flatpaks can't access other Flaptak's data folders in $HOME/.var/app (maybe even if home access is given?), but if given access to the "home" permission they can read and write to anywhere else in the user home, so stealing session cookies from a browser or ransomware could still be possible given the right permission. Modern apps that are designed to work as Flatpaks can use the xdg-desktop-portal to access only specific files/dirs upon user request, but it is only temporary access to a file. All the ways a Flatpak can access the system are defined by its permissions, so by giving more/dangerous permissions (such as devices or full filesystem access) a malicious app can possibly escape the sandbox and access arbitrary permissions. The worst permission an app can have is access to session bus for org.freedesktop.Flatpak, which allows it to arbitrary permissions, host command execution, and access to Flatpak configuration.

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  • [–] 2 points 11 months ago*

    There is more to xdg-desktop-portal than I said, it is quite powerful.

    https://wiki.archlinux.org/title/XDG_Desktop_Portal

    https://flatpak.github.io/xdg-desktop-portal/docs/

    This Flatpak shows the power of portals on your system, while also requiring no permissions at all: https://flathub.org/en/apps/com.belmoussaoui.ashpd.demo

    Same with this one, but it requires arbitrary permissions: https://flathub.org/en/apps/xyz.tytanium.DoorKnocker

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  • [–] 1 point 11 months ago (6 children)

    They also rely on the deprecated SUID-root binary FUSE2.

    There is no such thing as a suid fuse2, you are talking about suid fusermount, and libfuse2 which hasn't been true for 3 years the runtime is now static and doesn't depend on any libfuse (or any library) to work.

    And even back then it wasn't a hard dependency either, you could still run appimages by setting APPIMAGE_EXTRACT_AND_RUN=1 which makes them run without FUSE.

    The runtime still depends on a suid fusermount in PATH (it checks all the way to fusermount99 lol), however there is a much better runtime that does not FUSE to work at all since it can use mount namespaces instead.

    Meanwhile flatpak has a hard dependency on fusermount, it actually broke recently on ubuntu because they wanted to restrict access to fusermount.

    but if given access to the “home” permission they can read and write to anywhere else in the user home, so stealing session cookies from a browser or ransomware could still be possible given the right permission.

    web browsers (and electron apps) already have their own internal sandbox, which actually gets weakened by flatpak so it is actually not a good idea to be running those things with flatpak 1 2 3

    firefox recently finally got a fork server in linux, which means it is possible to at least get the zypack hack working with it, no idea if it has been implemented yet though.

    You also can sandbox appimages with bubblewrap, which is the very same sandbox flatpak uses, I wrote this tool used by AM for that.

    Apps will also have access to the portals, although I don't like this and looks like there is no easy way to disable access to portals other than disable all access to dbus which is bad.

    We already had an incident where someone thought there was a sandbox escape when it was just the app opening the portal xd

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  • [–] 1 point 11 months ago (1 child)

    I had heard of AM, and I actually stumbled upon your tool before. Thank you for the tool. I wish AppImage was updated to include sandboxing by default.

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  • [–] 2 points 11 months ago*

    AppImage is just a format, nothing is stopping distros from adding a binfmt_misc rule that makes all appimages be sandboxed with any tool. (this also means you can set this up so that they get executed inside a flatpak env btw)

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  • [–] 1 point 11 months ago (1 child)

    Yes, i understand that Flatpak weakens browser sandboxes, i was talking about the risk of a Flatpak which has access to user home and therefore could for example access $HOME/.firefox and steal session cookies.

    Also I based my assessment of use FUSE2 for normal AppImages on the security hardening used by Secureblue, mentioned here under the section "Filling known security holes"

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  • [–] 1 point 11 months ago

    i was talking about the risk of a Flatpak which has access to user home and therefore could for example access $HOME/.firefox and steal session cookies.

    Okay that makes sense.

    Also I based my assessment of use FUSE2 for normal AppImages on the security hardening used by Secureblue, mentioned here under the section “Filling known security holes”

    Remove the unmaintained and suid-root fuse2 by default.

    kek they got it wrong. Also:

    Mitigate LD_PRELOAD attacks via ujust toggle-bash-environment-lockdown.

    Interesting, I wonder if they prevent executing the ld-linux.so as well.

    There is two ways to preload libraries without having to modify the binary, the first is using LD_PRELOAD, the second is less well known but you can run binaries by calling the dynamic linker first (internally this is actually how all dynamic binaries you execute work btw) and then use the --preload flag to load a library.

    That is instead of:

    LD_PRELOAD=./kek.so /path/to/bin

    you do:

    /lib64/ld-linux-x86-64.so.2 --preload ./kek.so /path/to/bin

    I'm going to take a wild guess and assume the second is still possible in secureblue 👀

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