Thank you for your interest in improving the default experience in
Ubuntu.
We do understand that not everyone wants their machines to be talking to
the Ubuntu servers, which is why there are several ways to disable this
functionality.
- on a per-machine basis, you can set ENABLED=0.
- on a site-wide basis, you can firewall motd.ubuntu.com.
There is a factual inaccuracy in your report, which is to say that this
feature can be used to track login activity on machines. The update-
motd script in question contains the following check:
# If we're not forcing an update, and we have a cached motd-news file,
# then just print it and exit as quickly as possible, for login performance.
# Note that systemd should keep this cache file up to date, asynchronously
if [ "$FORCED" != "1" ]; then
if [ -r $CACHE ]; then
echo
safe_print $CACHE
else
: > $CACHE
fi
exit 0
fi
Thus, aside from a possible execution at first login, systems will only
contact motd.ubuntu.com twice per day with no correlation with user
logins.
It is also the case that Ubuntu systems already talk to Ubuntu servers
daily by default, as apt will check twice daily for updates from
archive.ubuntu.com and security.ubuntu.com, so the behavior of this
update-motd script in base-files is consistent with the existing
experience.
Finally, you've raised the concern that this script exposes information
about the system that could be used to exploit said system.
Canonical takes the security of Ubuntu users very seriously. This is
why, by default, security updates are applied to all Ubuntu systems
daily in 18.04. This is why we offer a kernel livepatch service that
enables users of Ubuntu 18.04 to fix high and critical kernel
vulnerabilities outside of scheduled maintenance windows.
If motd.ubuntu.com were ever to leak information to an attacker about
what machines on the Internet were vulnerable to a particular attack,
the root problem there would not be that information was shared with
motd.ubuntu.com; the root problem would be that Ubuntu machines
connected to the Internet had not had necessary security updates applied
to them. Because on the Internet at large, attackers do not wait for a
service like motd.ubuntu.com to tell them which machines are vulnerable
before exploiting them.
On the other hand, motd.ubuntu.com is a very important source of
information for US about what versions of Ubuntu are in use in the wild
- information that can be used, among other things, to identify problems
with the rollout of kernel security updates to our users.
So while it's understandable that some users will not want this
behavior, I believe that it is defensible as default behavior in Ubuntu.
--
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to base-files in Ubuntu.
https://bugs.launchpad.net/bugs/1832074
Title:
base-files '/etc/update-motd.d/50-motd-news' reports system use to
Ubuntu
Status in base-files package in Ubuntu:
Invalid
Bug description:
System information::
root@here $ lsb_release -rd
Description: Ubuntu 18.04.2 LTS
Release: 18.04
root@here$ dpkg -l base-files | tail -1
ii base-files 10.1ubuntu2.4 amd64 Debian base system
miscellaneous files
What I expect to happen::
Logins to my machine should not be communicated to anyone else, and
should not provide anyone else of information about my machine.
What does happen::
Logins to my machine report that a login occurred, and provide details
about the installed system, to Ubuntu.
Report::
I've just upgraded fromt Trusty to Bionic, and found that on login I
get a message telling me something about Ubuntu's Kubernetes. I don't
want advertising presented to me when I log in to MY system, so I
began to investigate where this is happening - assuming that /etc
/update-motd.d/10-help-text or 00-header had been updated during the
upgrade and recreated with this content.
Instead, I discover that there is another script that has been added -
/etc/update-motd.d/50-motd-news - which adds this junk text to the
login. Not only that, but the script comminucates with Ubuntu, to
fetch that information. Not only that, but it provides information
about the system that is running as part of the request.
During the upgrade, I was not asked about whether it was ok for the
system to call home every time I login (or every 12 hours, whichever
is sooner, but at least a minute after you boot), and it absolutely
would not be my expectation that this be the default. When I log in to
my machine, I do not expect that the event would be reported to any
off-site system, and I suspect that most other users would be
surprised if not horrified to find that the fact that a system is in
use was being reported to Ubuntu.
The service can be disabled by changing a setting in /etc/defaults
/motd-news from ENABLED=1 to ENABLED=0, but this almost certainly
should be defaulting to 0 - tracking disabled by default, not tracking
enabled by default.
For example, on my system this provides a user agent containing:
```
curl/7.58.0-2ubuntu3.7 Ubuntu/18.04.2/LTS GNU/Linux/4.15.0-50-generic/x86_64
Intel(R)/Xeon(R)/CPU/X5675/@/3.07GHz uptime/580915.35/4598709.84
```
This means that every time the user logs in (or after 12 hours from
the prior log in, whichever is longer) Ubuntu receives:
* The IP address of a system that is in use (which might be behind NAT, but
it's still a report).
* The Distribution version details.
* The Kernel version details
* The CPU type
* The uptime
Knowing where a machine is, that it is active, exactly what type of
system it is an how often it is restarted, would be an awesome dataset
for any attacker to obtain - ideally (for them) it tells them the
location of systems that are alive, how they might be attacked - from
the distribution version, the kernel and the CPU information, you can
determine a set of vulnerabilities to attack - and the uptime, which
will indicate how likely the system is to be patched.
The only thing that might be worse might be to include a cookie-jar on
the curl command, which would allow tracking of individual systems,
rather than aggregating them behind NAT using the IP (although it's
still possible that the data reported in the user agent may be able to
make that information individually usable). That said, the root user
could (unintentionally) enable a cookie jar in their .curlrc and thus
enable individual system tracking without realising.
Whilst there may be legitimate reasons for reporting this information
(say for reporting to the user that their system has updates available
or that the system is vulnerable!), an advertising tool which reports
the system's information regularly back to home does not seem
appropriate for a 'base-files' package.
The surprise at having my logins recorded on a remote site pales in
comparison to the horror of recording a database of systems that might
be abused.
The Privacy and potential Security concerns of this feature hugely
outweigh any perceived benefit to the user, and I believe that the
right course of action is to remove this script entirely from the
distribution. At the very least the script's operation should default
to being disabled.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/base-files/+bug/1832074/+subscriptions
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