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Ubuntu Security Podcast

Episode 155

33 min • 1 april 2022

Overview

It’s an off-by-one error in the podcast this week as we bring you part 4 of Camila’s 3-part Ubuntu hardening series, plus we look at security updates for Thunderbird, OpenVPN, Python, Paramiko and more.

This week in Ubuntu Security Updates

47 unique CVEs addressed

[USN-5345-1] Thunderbird vulnerabilities [00:45]

[USN-5346-1] Linux kernel (OEM) vulnerability [01:21]

  • 1 CVEs addressed in Focal (20.04 LTS)
  • ICMPv6 memory leak - DoS via remote unauthenticated user

[USN-5353-1] Linux kernel (OEM) vulnerability

  • 1 CVEs addressed in Focal (20.04 LTS)
  • Heap buffer overflow in IPsec when doing ESP transformations - not remotely triggerable, requires local user -> DoS/privesc

[USN-5347-1] OpenVPN vulnerability [02:00]

  • 1 CVEs addressed in Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10)
  • Possible authentication bypass through only partially correct credentials due to use of multiple plugins which do deferred authentication - updated to only allow one plugin to do deferred auth

[USN-5321-3] Firefox regressions [02:42]

[USN-5342-1] Python vulnerabilities [02:54]

  • 3 CVEs addressed in Trusty ESM (14.04 ESM), Xenial ESM (16.04 ESM), Bionic (18.04 LTS), Focal (20.04 LTS)
  • pydoc server could disclose other files - shouldn’t be exposed to untrusted users
  • Mishandling of FTP requests (could be tricked into connecting to wrong server)
  • urllib.parse mishandled URLs with embedded newlines - possible to bypass regular checks leading to possible URL/request injection etc

[USN-5348-1] Smarty vulnerabilities [03:42]

[USN-5349-1] GNU binutils vulnerability [04:17]

  • 1 CVEs addressed in Xenial ESM (16.04 ESM)
  • gold linker - not the default linker in Ubuntu (would have to specify it manually via -fuse-ld=gold to gcc)
  • OOB read when handling a crafted ELF file

[USN-5352-1] Libtasn1 vulnerability [04:42]

  • 1 CVEs addressed in Xenial ESM (16.04 ESM)
  • CPU based DoS on crafted ASN.1 input

[USN-5351-1, USN-5351-2] Paramiko vulnerability [05:11]

  • 1 CVEs addressed in Xenial ESM (16.04 ESM), Bionic (18.04 LTS), Focal (20.04 LTS), Impish (21.10)
  • Race condition between creating a then setting permissions on the private key file allows a local attacker to possibly read the private key - fixed to simply create the file with the restricted permissions in the first place

[USN-5313-2] OpenJDK 11 regression [05:55]

[USN-5350-1] Chromium vulnerability [06:17]

  • 1 CVEs addressed in Bionic (18.04 LTS)
  • Thanks to Olivier Tilloy (oSoMoN) from Desktop team

Goings on in Ubuntu Security Community

Camila discusses Ubuntu hardening (part 4 / follow-up) [06:43]

  • Follow-up to the previous 3 part series on Ubuntu hardening (Episode 154, Episode 153, Episode 152)
  • Minor improvements and corrections to the various tips presented over the past few episodes

Transcript

Hello listener! Welcome back to our Ubuntu hardening journey in the Ubuntu Security Podcast. Hey! I know what you’re thinking: I can’t count. I said this would be a three part series…and well…here I am in a fourth episode talking about this again. You could also be thinking “Hey, you’ve got the wrong title there…what’s the new topic for this episode?”, and should this be any other situation, I might’ve said you are right to either one of these two assumptions because I can be a bit of a scatterbrain sometimes. But not this time! I am here today once again talking about Ubuntu hardening because, hey…cyber security is a continuous effort. Remember that? And you know what also is a continuous effort? Learning and becoming wiser, and in our journey to do so, it is very likely that we will make a few mistakes here and there, myself included. Ok, ok, I’ll stop rambling and saying pretty words to distract you from the real deal here: I might’ve made some mistakes…Ooops! I apologize. Because yes, I do know about cyber security, but I am definitely not the master of all when it comes to it. So, in the past three episodes there were some sentences here and there that might have been a little bit incorrect, and some other sentences that might have been forgotten to be said. BUT WORRY NOT! I am here today to fix this. I got a review on my script for the last three episodes made by another one of the security team members, and they gave me a lot of helpful feedback on what I said and on what I suggested to you all. Since I had already recorded the other episodes and my laziness spoke a little higher than my willingness to spend the day re-editing audio files, I decided to instead bring a new episode to you. Coincidentally, recording a part 4 to a previously established 3 part series really resonates with the vibe that is the hardening process of an operating system: we want to always review our work, and fix mistakes whenever possible. Maintain and evolve, even if we do hit a few bumps on the road and make some mistakes along the way. We are human after all, and even if the computer isn’t, all that it does is do what we ask of it, so…yeah! Enough introductions, let’s move on to the meat and potatoes of this episode and right some wrongs! Oh…actually…I don’t think it is really necessary to mention this…but there is always that one person, so: listen to the other episodes if you haven’t yet. I can’t really fix something that you don’t even know is broken.

Ok, point number one that was brought to my attention: remember when we were talking about the swap partition in part 1? Well, it is a valid solution for all the reasons that I mentioned there, but it is not the only one. Drumroll please, as I introduce you all, if you don’t already know it, to the swap file. TADA! The swap file, as the name suggests, is a file in your system that will serve the same purpose as a swap partition. However, instead of being configured as a separate partition of your disk, a swap file is created under the root partition in your system and you simply nudge the OS to remind it that that specific file should be used as swap whenever necessary. Neat, right? Specially because resizing swap files is a lot easier than resizing an entire swap partition. A LOT easier. Using command ‘fallocate’ or command ‘dd ‘will help you get a swap file ready in case you wish to use this method of swapping instead of creating an entire new partition during install, or in case you forgot about it during install. Use the ‘mkswap’ tool to tell Ubuntu that the new file is a swap space and enable the swap file with ‘swapon’. To finish it off, and make changes permanent, add information on the swapfile to ‘fstab’. Remember to correctly set permissions in this swap file, as, even though it is a swap entity, it is still a file. Only the root user should be able to write to that file or read from it, so get your ‘chmod 600’ ready for that. The conclusion here is: both a swap partition and a swap file will serve the same purpose, and they are both located on disk, so not much to compare on that front. However, if you are looking for something more flexible, stretchy, if you will, consider using the swap file. It will help you out with your maintainability needs, and with adjusting to changes in the future, especially if these changes involve increasing the size of the swap, or decreasing it due to hardware changes applied to your device, or any other type of related changes. I do stress though, hopefully enough that you are just being reminded of this here: do this if it suits YOUR needs. Maybe you already have a swap partition, and it is ok to you for it to have an immutable size until the end of eternity, and that is great! You do you. What is important for you to takeaway here is that I am giving you another option, one that might better suit your needs, or not, but I am not the one to decide that for you.

Next up, let’s talk about that ‘hidepid=2’ suggestion I made in part 2, shall we? This suggestion came up when we were talking about fstab, and I was telling you about ways to protect your /proc directory from the prying eyes of possibly malicious users. Well, it unfortunately doesn’t work when you have systemd installed, which is the case for Ubuntu. Whewhe. So yes, blame me for relaying possibly incorrect information to you. I am deeply sorry…but please don’t cancel me for it. There are a few bug threads that mention this error and a lot of proposed solutions given by the community can be found in the various comments. I will not go into too much detail on those here because it might be a bit difficult to get the actual solution through without any visual aid, but I do encourage you to do some research on this, and maybe apply one of the suggested alternatives should it be adequate for your system. Sorry once again for giving you a hardening tip that would cause an error in your system, but hopefully the solutions out there will allow you to get right what I initially got wrong. I’ll try to get some links containing some of these solutions added to the podcast notes in order to help you out, and in order to atone for my mistakes. I’m sorry, I’m sorry once again. Ok, I’ll stop now.

Point number three: I told you to love your logs and embrace your logs during part 2 of this series. The computer pours out its innermost secrets to you and you decide to ignore it? Well…I kind of ignored it a little bit as well, because I talked so much about ‘syslog’ and all of its log files that I forgot about another oh so very important member of the logging squad: ‘journald’. If your Linux system has ‘systemd’, it does have ‘journald’, and therefore, if you are using Ubuntu, you most likely have it too. Since ‘journald’ stores data in binary format, the usual way of accessing the data it collects is not recommended here, as our brains have still not yet evolved to immediately read and process unreadable characters when looking at a sequence of those characters. There are no plain text log files here. Instead, if you want to check out all of the logging goodness that ‘journald’ can provide, and expose all of your device’s secrets, you have to use the ‘journalctl’ utility. I am pretty sure this name is familiar to you, as most times when you have a service issue in Ubuntu or a system issue in general, it recommends you check out the output of ‘journald’ by typing in a shell ‘journalctl -x’. ‘Journald’ is a very interesting logging tool and it can allow you to troubleshoot your system very efficiently. It tracks each log to a specific system boot, for example, and this means that you can check logs considering only data connected to a specific boot instance when using the ‘-b’ option. So, if you have a situation where you know that the issue happened the last time you turned on your computer, instead of checking all of the log, you can narrow it down and try to find your problem in fewer lines of log data instead. You can also filter log data based on a time range, based on a specific service, based on a specific user or based on message priority level. Which one is better to use between ‘syslog’ and ‘journald’, you ask? It depends on your needs. Advantages of using ‘journald’ include the fact that it structures data in such a way that searches can be optimized, plus, it indexes data, meaning that lookup operations of the log files will happen in a much faster manner than they would when searching for information in plain text files. Filtering is also easier with ‘journald’, as seen by all of the options I mentioned previously that you can use together with ‘journalctl’. With ‘syslog’ and all its different plain text log files, it might be a little bit more difficult or troublesome to find exactly what you are looking for, and even correlate log information without having a third party software to maybe assist you with this job. When searching through ‘syslog’ logs we usually end up using ‘grep’, our handy-dandy text file search tool, but unfortunately, ‘grep’ will not take into account the context of a situation. So, when searching through ‘syslog’ logs, instead of a simple one line command you would type if using ‘journalctl’, you create a huge multiline beast with a lot of pipes to get a coherent and valuable result out of the many ‘syslog’ files you wish to have analyzed. Another advantage of ‘journald’ is that ‘journald’ has permissions associated to its log files, so every user is able to see their own log without actually being able to see output that would be exclusive only to root, for example, said users needing to prove their privileged identity before accessing this other sensitive data about the system. Therefore, regular users are able to troubleshoot using ‘journald’ logs, but at the same time, information that should not be exposed to regular users for one reason or another is protected. With ‘syslog’ it will all depend on permissions associated to the log text files, and these will include ALL of the information for one specific log source, so it won’t be every random user that will have the opportunity to possibly use log data to solve their issues, unless you allow said random user to actually read logs in their entirety. Talking a bit about possible disadvantages related to ‘journald’: ‘journald’ does not include a well-defined remote logging implementation and, therefore, is not the best option to consider when you need to build a central logging server, whereas ‘syslog’ allows that to happen very well, since there is even a same name protocol which is used to send messages to a main log server running a ‘syslog’ instance. Plus, ‘journald’ considers only information of Linux systems, while ‘syslog’ encopasses more, such as logs generated by firewall devices and routers. This means that correlation between the logs of the different devices in your infrastructure might be made more efficient when you indeed have a centralized ‘syslog’ server to gather all of that information, especially considering that it is possible to send ‘journald’ data to an already existing ‘syslog’ implementation, as ‘journald’ retains full ‘syslog’ compatibility. One of the issues we find with this though, is that most advantages that come with ‘journald’ are lost when such messages are sent to the centralized ‘syslog’ server, as this server, as the name implies, will include a ‘syslog’ implementation instead of a ‘journald’ one, this ‘syslog’ implementation recovering, storing and processing messages as a regular ‘syslog’ instance would…so, no indexing and no optimized data reading and filtering. The other possible issue is that ‘journald’ needs to send its data to a local ‘syslog’ server, and this server will then send that data to the remote one. Having two tools doing the same logging work might not be the most ideal thing for you or your infrastructure, so do take that into account when setting up your logs and your whole logging system. For this reason and the other reasons mentioned we have that ‘journald’ ends up being more “host-based” than ‘syslog’. Therefore, I once again ask the question: which one is better to use? Maybe it’s ‘journald’ in case you have one host only, maybe it’s ‘syslog’ if you have an entire infrastructure and a centralized log server with third party software that processes all information it gets, or maybe it’s even both, since, as we already discussed in previous episodes, an extra layer of protection is what will help you build up your cyber security walls of defense more efficiently, especially when you consider that you already have ‘journald’ installed by default in your system.

Going on to point number four: when installing tools such as Rootkit Hunter, be aware of possible false positives. It is always useful to have tools that scan your system for you, and point you towards the direction issues might be, however, it is interesting to confirm that the issue database used by such programs is updated and well matched to your system in order for results to be actually useful. So keep two things in mind: that tools such as Rootkit Hunter exist and can be very helpful, and that, even though they can be helpful, they can also not be if they are out-of-date and just end up flooding you with false positives that will then lead you on a wild goose chase that generates nothing of value to you or your system. Also, do be careful about installing programs such as vulnerability scanners that can be later on used by attackers themselves to find flaws in your system. If you’ve used it and no longer need it installed, maybe remove it until it is once again necessary…after all, even security tools increase the attack surface of your system, and they themselves might have vulnerabilities related to them that could be exploited by someone with enough knowledge of it. Finally - and me saying this might sound unnecessary because it should be obvious, but I do say it because there is always that someone out there…right? - don’t think that a scan performed by ONE single scanning tool is enough to guarantee security of a device, especially when we consider tools that do need to rely on previously known hashes, or rules, or sets of steps, in order to identify a possibly malicious entity in a system. That is because attackers are always trying to circumvent these tools by using digital fake mustaches, and, sometimes, these disguises are enough, as is a certain superhero’s glasses. I mean…how can people not know they are the same person? Unfortunately, this major oversight might happen sometimes with your security tools as well, so knowing this is key in order to actually build a truly secure system. By knowing, you also know that said tools should only be a part of a bigger, LAYERED strategy you use to harden your system. Agreed?

Time to dive into point number five. I was asked a question: is ‘ping’ still ‘setuid’ root? And the answer is actually “no”. Oh, well! Remember when we were talking about the dangers of the ‘setuid’ binaries and I used ‘ping’ as an example to show the issues that might arrive when you set that sneaky permission bit to 1? Well, it turns out that my example was a little bit outdated, since ‘setuid ping’ was already put in the WANTED list for “causing too many security issues” and was therefore demoted to non-‘setuid’ status. So, if you are using Ubuntu 20.04 LTS, for example, you can run an ’ls -la /usr/bin/ping’ and you will see permissions set to 755 instead of 4755. How is the privileged socket access performed in this case? Ah…well, that might be a discussion for a future podcast episode, especially since a little bird told me that the solution for that might have caused an even bigger issue than the ‘setuid’ bit when changes to remove it were initially being made. For now, I’ll just leave you to wonder a little bit more about this, and reinforce that, even if ‘ping’ is no longer ‘setuid’, the example stands to show the dangers of having this bit set, be it ‘ping’, be it any other executable in your system that might allow for malicious tampering. Consider the ‘ping’ example a template of what COULD happen should you decide to maybe set its ‘setuid’ bit. Don’t actually do that though, please.

Point number six is as simple as: ’netstat’ has been replaced with ‘ss’. I mentioned using ’netstat’ to check open ports in your system because that is what I have been using since forever. Old habits die hard, I guess…and that, my friends, is definitely something I shouldn’t be saying here, because old habits will also compromise you, since it is always important to keep up-to-date with recent software if you plan on being secure. So yes, forgive me for I have been a hypocrite. Information on ’netstat’ being deprecated is even in the ‘man’ page for netstat. Oof…hurts to see my own mistakes. Read your manuals people, their existence is not trivial. But, you know what? You live and you learn. I know better now, and you do too. So let’s be better together, friends, and use ‘ss’ instead of the obsolete ’netstat’ to find open ports in our system that are open for absolutely no reason! The good thing to come out of this mistake is that we get to once again remember the importance of updating and maintaining systems in order to actually keep them secure, and this also includes the system that is our own minds.

Ok, now that we have tackled the ahem minor errors I made in the last few episodes, and honorably mentioned applications I forgot about, let’s bring up a few other hardening suggestions made by the Ubuntu Security Team so that you can harden your system even more!

Let’s start with the Mozilla TLS configuration generator: this tool which can be accessed through the “https://ssl-config.mozilla.org/” URL can be used to generate configuration files for various server programs, Apache and Nginx included, and it considers three different security levels! Pretty nifty, and gives you the opportunity to maybe learn more about application settings you might not have known all that much about in the first place, and how they can help you when you wish to do hardening for applications you use.

Let’s Encrypt is in this list as suggestion number two, and it is a tool that allows you to get certificates and renew them often enough that you can’t have expired certificates ruin your day. Let’s Encrypt is a CA, or, expanding on the acronym, a Certificate Authority, which is an entity you will need if you plan on using TLS to encrypt your web server’s communications, for example. You can use Let’s Encrypt to create your certificates and then configure the tool to automatically update these certificates whenever they are close to expiring. Phew! No need to worry about unintentionally sending unencrypted data over the wire because of a missed expired certificate! Give those attackers NO windows of opportunity!

AppArmor is installed in Ubuntu by default, and we already talked about it in the last episode, but I am here to ensure that you remember that it does exist, and, even better, you don’t even have to install it in your Ubuntu system to start using it. Take advantage of its existence and don’t forget to profile applications running in your system! Profile ’til you can’t no more and get that metaphorical armor polished and ready to take on everything and everyone, just because you can.

And last but not least, I can’t NOT reinforce this, as I am in the security team and this is what we do for you: always install your updates. Always! It might seem annoying, it might take some of your time, it might even be a little bit angering…but isn’t making changes for the better what life is all about? Update and live to see your server survive another day! Update and sleep peacefully knowing that you are doing the best you can for that server you care about! Update and be ready! Some updates will require the restarting of services, so that those actually start using patched versions of recently changed libraries, and, when we are talking about the kernel, reboots might be necessary, so include restarting and rebooting in your update plans as well, or else the patching done by the security team won’t be effective in your system. If you are having trouble with this…shameless plug: consider using Ubuntu Livepatch in order to get those kernel security-critical updates installed into your system without having to reboot the machine! It’s free for personal use on up to three computers, and it is easy to set up through your Ubuntu system with your Ubuntu One account.

And that is it! An extra episode to patch my previous mistakes, and to deliver to you updates on some previously incomplete information! An episode that mirrors the work done by the Ubuntu Team on its packages, and that hopefully brings you as many benefits as those patches do! Keep your patches up to date, keep your hardening up to date, keep your knowledge up to date, and I am sure you will be ready to face a lot more than you expect! Thank you all for listening to this extra episode of the Ubuntu hardening series on the Ubuntu Security Podcast. Feel free to share your thoughts on this subject and on this series in any of our social media channels! I hope to talk to you all once again in the future, but for now, I bid you farewell and until next time! Bye!

Ubuntu 22.04 Beta Released

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