If you’re running Ubuntu and/or using snaps, look into CVE-2020-27348

I was reading an article about CVE-2020-27348 earlier, which is quite a nasty bug affecting a lot of snap packages.

My desktop runs Ubuntu 18.04 at the moment, and so does my partner’s laptop. I also have a Debian buster laptop but I’ve never installed snapd there. So it’s just my desktop and my partner’s laptop I’m concerned about.

If you run Ubuntu 20.04 or later I think there’s probably more concern, as I understand the software centre offers snap versions of things by default.

Anyway, I couldn’t recall ever installing a snap on purpose on my desktop except for a short while ago when I intentionally installed signal-desktop. But in fact I have quite a few snaps installed.

$ snap list
Name                  Version                     Rev    Tracking         Publisher     Notes
core                  16-2.48.2                   1058   latest/stable    canonical✓    core
core18                20201210                    1944   latest/stable    canonical✓    base 
gnome-3-26-1604             100    latest/stable/…  canonical✓    -
gnome-3-28-1804       3.28.0-19-g98f9e67.98f9e67  145    latest/stable    canonical✓    -
gnome-3-34-1804       0+git.3556cb3               66     latest/stable    canonical✓    -
gnome-calculator      3.38.0+git7.c840c69c        826    latest/stable/…  canonical✓    -
gnome-characters      v3.34.0+git9.eeab5f2        570    latest/stable/…  canonical✓    -
gnome-logs            3.34.0                      100    latest/stable/…  canonical✓    -
gnome-system-monitor  3.36.0-12-g35f88a56d7       148    latest/stable/…  canonical✓    -
gtk-common-themes     0.1-50-gf7627e4             1514   latest/stable/…  canonical✓    -
signal-desktop        1.39.5                      345    latest/stable    snapcrafters  -

I don’t know why gnome-calculator is there. It doesn’t appear to be the binary that’s run when I start the calculator.

So are any of them a security risk? Well…

$ grep -l \$LD_LIBRARY_PATH /snap/*/current/snap/snapcraft.yaml

Those are all the snaps on my system which include the value of the (empty) environment variable LD_LIBRARY_PATH, so are likely vulnerable to this.

But does this really end up with an empty item in the LD_LIBRARY_PATH list?

$ which gnome-system-monitor 
$ gnome-system-monitor &
$ pgrep -f gnome-system-monitor
$ tr '\0' '\n' < /proc/8259/environ | grep ^LD_LIBR | grep -q :: && echo "oh dear"
oh dear

Yes it really does.

(The tr is necessary above because the /proc/*/environ file is a NUL-separated string, so that modifies it to be one variable per line, then looks for the LD_LIBRARY_PATH line, and checks if it has an empty entry ::)

So yeah, my gnome-system-monitor is a local code execution vector.

As are my gnome-characters, gnome-logs and that gnome-calculator if I ever uninstall the non-snap version.

That CVE seems to have been published on 3 December 2020. I hope that the affected snaps will be fixed soon.

I don’t like that the CVE says the impact is:

If a user were tricked into installing a malicious snap or downloading a malicious library, under certain circumstances an attacker could exploit this to affect strict mode snaps that have access to the library and were launched from the directory containing the library.

My first thought upon reading is, “I’m safe, I haven’t been tricked into downloading any malicious snaps!” But I do have snaps that aren’t malicious, they are just insecure. The hardest part of the exploit is indeed getting a malicious file (a library) into my filesystem in a directory where I will run a snap from.

Disabling edge tiling on GNOME 3.26 / Ubuntu 17.10

Edge tiling? ^

It’s that thing where when you drag a window so it hits the edge of the screen, GNOME offers to maximise the window. Generally the number of times I will knowingly want to maximise a window by dragging it to the top of the screen is 0, while the number of times it happens accidentally is over 9,000 by lunch time.

Things that work ^

$ dconf write /org/gnome/mutter/edge-tiling false

It should take effect immediately.

If you like a pointy clicky way to do it then install dconf-editor package and run dconf-editor, but really all you will do is click down the tree orggnomemutter and then toggle edge-tiling so I don’t really see the point.

Things that people on the Internet say work, but don’t – a non-exhaustive list ^

These suggestions silently fail to do anything, as far as I can see. They may have been correct for earlier versions of GNOME, but I am using GNOME on Ubuntu 17.10 and they didn’t work for me.

dconf write /org/gnome/shell/extensions/classic-overrides/edge-tiling false
gsettings set org.gnome.shell.overrides edge-tiling false
dconf write /org/gnome/shell/overrides/edge-tiling false

Supermicro IPMI remote console on Ubuntu 14.04 through SSH tunnel

I normally don’t like using the web interface of Supermicro IPMI because it’s extremely clunky, unintuitive and uses Java in some places.

The other day however I needed to look at the console of a machine which had been left running Memtest86+. You can make Memtest86+ output to serial which is generally preferred for looking at it remotely, but this wasn’t run in that mode so was outputting nothing to the IPMI serial-over-LAN. I would have to use the Java remote console viewer.

As an added wrinkle, the IPMI network interfaces are on a network that I can’t access except through an SSH jump host.

So, I just gave it a go without doing anything special other than launching an SSH tunnel:

$ ssh me@jumphost -L127.0.0.1:1443: -N

This tunnels my localhost port 1443 to port 443 of as available from the jump host. Local port 1443 used because binding low ports requires root privileges.

This allowed me to log in to the web interface of the IPMI at https://localhost:1443/, though it kept putting up a dialog which said I needed a newer JDK. Going to “Remote Control / Console Redirection” attempted to download a JNLP file and then said it failed to download.

This was with openjdk-7-jre and icedtea-7-plugin installed.

I decided maybe it would work better if I installed the Oracle Java 8 stuff (ugh). That was made easy by following these simple instructions. That’s an Ubuntu PPA which does everything for you, after you agree that you are a bad person who should feel badaccept the license.

This time things got a little further, but still failed saying it couldn’t download a JAR file. I noticed that it was trying to download the JAR from even though my tunnel was on port 1443.

I eventually did get the remote console viewer to work but I’m not 100% convinced it was because I switched to Oracle Java.

So, basic networking issue here. Maybe it really needs port 443?

Okay, ran SSH as root so it could bind port 443. Got a bit further but now says “connection failed” with no diagnostics as to exactly what connection had failed. Still, gut instinct was that this was the remote console app having started but not having access to some port it needed.

Okay, ran SSH as a SOCKS proxy instead, set the SOCKS proxy in my browser. Same problem.

Did a search to see what ports the Supermicro remote console needs. Tried a new SSH command:

$ sudo ssh me@jumphost \
-L127.0.0.1:443: \
-L127.0.0.1:5900: \
-L127.0.0.1:5901: \
-L127.0.0.1:5120: \
-L127.0.0.1:5123: -N

Apart from a few popup dialogs complaining about “MalformedURLException: unknown protocol: socket” (wtf?), this now appears to work.

Supermicro IPMI remote console

SSH launchers for Ubuntu Unity

Ubuntu 12.04 ^

Given the recent release of Ubuntu 12.04, I thought it was about time that I upgraded one of my machines to it so that I could make sure I could still work with it effectively.

You see, both my laptop and my desktop were on the previous long term support release, 10.04. These days I don’t have a lot of patience for upgrading things every 6 months so I’m glad that the LTS releases are supported for many years. But after 10.04 Ubuntu made a bold departure away from the GNOME desktop and onto Unity. Knowing that I would be forced to change the way I did many things I have been putting off trying Unity. No more putting it off.

Terminals, Terminals, Terminals, Terminals, Terminals, Terminals ^

Given what I do for a living it’s fair to say that the predominant applications running on any of my desktop machines are many instances of terminals running SSH to remote hosts. I try to automate and configuration manage the hell out of everything, but it’s hard to avoid having connections open to a bunch of different machines at any one time.

In 10.04 what I used to do was have a .desktop file for each host that I commonly log in to, something like:

#!/usr/bin/env xdg-open

[Desktop Entry]
Exec=urxvtc -T specialbrew -e ssh specialbrew.localnet

I’d then have a menu called “SSH” added to my top menu bar, with an entry for each of those files. This was quite nice as I could also have multiple levels of menu, thus segregating different classes of host, hosts I administer with different hats on, customers I do consulting work for, etc.

Unity’s Launchers ^

Sadly that all goes out of the window with Unity. For a start there is no top menu bar. You’ve got the launcher down the side where you can add the launcher for gnome-terminal, but if you click that launcher more than once all that happens is you get your first terminal window brought back to focus.

There’s an open bug report asking for ways to set different properties on launchers, but judging by the age it doesn’t seem to be much of a priority.

I haven’t got a clue about launchers in Unity but I had a quick read of some documentation and worked out how to add a launcher for urxvt (my preferred terminal as opposed to gnome-terminal), and how to put different options on it. For example:

$ cat ~/.local/share/applications/rxvt.desktop 
[Desktop Entry]
Comment=Use the command line

[Desktop Action New]
Name=New Terminal (localhost)
Exec=/home/andy/bin/urxvtc -T stoli

[Desktop Action specialbrew]
Name=New Terminal (specialbrew)
Exec=/home/andy/bin/urxvtc -T specialbrew -e ssh specialbrew.localnet

[Desktop Action backup1]
Name=New Terminal (backup1)
Exec=/home/andy/bin/urxvtc -T backup1.bitfolk.com -e ssh backup1.bitfolk.com

Once you do something like that and get the icon locked on the Launcher, you can right click on it and be offered “localhost”, “specialbrew”, “backup1”, etc.

Okay that is workable, but it kind of sucks. That list will get huge, and it’s a flat list.

Lenses ^

Lenses seem like a very powerful feature of Unity. When I was asking on IRC about how people handled this use case, someone suggested (sarcastically, I think!) that I needed to create a lens to view all my hosts.

I actually did have a look into it, and was initially rather put off by the task. Fortunately it seems that someone already had the idea of a lens that scrapes SSH hosts out of ~/.ssh/config and ~/.ssh/known_hosts.

The SSH Search Lens ^

After installing this, it worked pretty much as advertised. As noted in the README you do have to use “HashKnownHosts no” to take advantage of it being able to read ~/.ssh/known_hosts — some would consider that a security flaw. Rather than disabling known host hashing for all users, you can disable it just for yourself:

$ cat ~/.ssh/config
HashKnownHosts no

Note that it only re-parses the SSH configuration files when it starts, which means that if you SSH to somewhere new then it won’t be found in Dash Home until after you’ve logged out and in again (officially). I found that looking for the /usr/bin/python /opt/extras.ubuntu.com/unity-lens-sshsearch/unity-lens-sshsearch.py process and killing it would cause it to be restarted next time I went to Dash Home. That saves a logout/in (but might be Bad).

The current version is hardcoded to call gnome-terminal, and I wanted to change that. I edited /opt/extras.ubuntu.com/unity-lens-sshsearch/unity-lens-sshsearch.py and changed the following line:

TERMINAL_APP = 'gnome-terminal'


TERMINAL_APP = '/home/andy/bin/urxvtc'

(Yes, I compile rxvt-unicode from source and keep it in ~/bin. What of it? Wanna fight about it?)

After restarting the lens it failed to work. Nothing happened when clicking on the icons it found. It wasn’t sending anything to ~/.xsession-errors either.

In the end I had to strace it, only to find it was getting “permission denied” when trying to execute my TERMINAL_APP. What? I can execute it myself.


Yeah, unity-lens-sshsearch ships an AppArmor profile, /etc/apparmor.d/opt.extras.ubuntu.com.unity-lens-sshsearch.unity-lens-sshsearch.py to be exact. That specifies what it can execute, and it’s limited to gnome-terminal.

After adding the paths to my rxvt-unicode there (it’s pretty obvious how, if you look in the file) it was happy.

Deficiencies of the SSH Search Lens ^

So, obvious deficiences here:

  • Have to log out or risk killing the process to get it to index newly-added entries.
  • Hard-coded to gnome-terminal.
  • Still limited in terms of configurability to <command>, <user>, <host> and <port>
  • Still has a flat hierarchy — you’ve got a list of hosts that your search term will be matched against. Possibly greater knowledge of Lenses/Scopes could improve this.
  • My rxvt-unicode doesn’t have a nice icon like gnome-terminal does! I’m guessing I will be able to fix this by reading up more about the Launcher.
  • Would be nice if the stderr output of the lens went to ~/.xsession-errors like every other X application, instead of /dev/null that I note it is redirected to. I realise that ~/.xsession-errors tends to be known as “that multi-gigabyte file of garbage that no one ever looks at” but it’s marginally more useful than /dev/null!

But on the whole this is a fairly natural way for me to launch these SSH sessions — I can press the “super” key and start typing the host name and I’ll get a list of matching icons to click on.

Also even though I don’t know Python, the source of this lens seems quite readable so I may be able to improve it and/or make my own lenses in future.

Firefox, Ubuntu and middlemouse.contentLoadURL

I use Firefox web browser, currently on Ubuntu 10.04 LTS. For many years I have set the config option middlemouse.contentLoadURL to true so that middle clicking anywhere in the page (that does not accept input) will load the URL that is in my clipboard.

After restarting my web browser somewhere near the end of January 2012 I found my Firefox 3.x had been upgraded to Firefox 9.x. Also the middle click behaviour no longer worked.

Perusing about:config showed that the option had been set to false again. I set it back to true but on restart of the browser it was set back to false. A bit of searching about found various suggestions about forcing it in my user.js file, but none of those worked either.

Finally, in desperation, I did a search of every file beneath /usr for the string “middlemouse”. Lo and behold:


pref("middlemouse.contentLoadURL", false); //setting to false disables pasting urls on to the page

Commenting this line out once more allowed me to change the setting myself.

It seems this this override was discussed by Ubuntu as far back as 2004, but it only became something that I could not override upon the upgrade to Firefox 9.

I reported a bug about this, and one of the comments seems to suggest that the method Ubuntu uses to change these settings has changed because they were breaking Firefox Sync, and that this outcome (overriding middlemouse.contentLoadURL) is not as bad as breaking Firefox Sync.

Even so, I would suggest that this outcome is very confusing for people and that as middlemouse.contentLoadURL is a popular setting which is easy to change, it should not be overridden in some obscure file.

As of the recent upgrade to Firefox 11, the file with the override in it has now moved to /usr/share/xul-ext/ubufox/defaults/preferences/ubuntu-mods.js.

Win a BitFolk VPS on the Ubuntu UK Podcast!

As well as sponsoring one of the mirrors, BitFolk has contributed a prize in the most recent episode of the Ubuntu UK Podcast, released on Saturday 30th August.

The prize is £200 of service credit with BitFolk, so for example the winner could put it towards a 300M VPS for one year or a 120M for over two years. Even existing customers should feel free to enter. You’ll have to listen to the podcast episode to find out the competition question and instructions for entering.

There is also an informative discussion of virtual server technology in general, so give it a listen.


Two mirrors for Ubuntu UK Podcast

BitFolk is providing additional mirrors in London and San Francisco for the Ubuntu UK Podcast.

I think my end is sorted out so hopefully the Ubuntu UK side of things will be ready in time for episode 2’s release early next week.

Obviously as it’s only on episode 2 it’s rather new so I’m not exactly expecting a deluge of requests, but it will be interesting to see actually what bandwidth is used.

(click images for more detail; if image is broken then the graph is currently updating)