Adventures in Open Source Software: Dealing with Security

I had the opportunity to give this talk at the London chapter of DefCon, DC4420 and censecutivily at London Perl Mongers technical meeting last week.
The subject of the talk was all the factors outside of doing security resceach which can make the process of dealing with advisories a daunting or a seamless process. As observed during the last year, while working as part of a security team.

Slides

Intro:
pkgsrc is a crossplatform packaging system by the NetBSD project, forked from the FreeBSD ports in the late 90’s, initially the primary target was NetBSD but with the portability focus of the project, the list of supported flatforms has grown to a list of 23 operating systems (16 out of those 23 are currently actively worked on). Within the pkgsrc project, there is a dedicated security team whose responsibility is to audit published vulnerabilities and ensure that those which apply to software we offer packages for are listed in a file. Users download this file & use it to check their installed packages.
Other open source projects have teams who are more involved and participate in the security research process and publish their own advisories, such as Debian or Redhat but that is not  main focus of our team.
There may be several reasons for this, during my talk I refered to the aquisition of a security company by Redhat, but looking up Redhat on Wikipedia, there doesn’t appear to be anything to suggest that.
I can say that for the pkgsrc-security team, the role is focused on filtering information and ensuring that items are listed in the pkg-vulnerabilities file, maintainers are notified (if there is one) and co-ordinating with the release engineering team so that necessary commits are pulled into the relevant branches. This is because we try to avoid dealing with development within our tree and opt to co-ordinate with upstream to submit fixes. Majority of our changes focus on removing assumptions to ensure things are built in a consistent manner and allow the software to be packaged how we like.

Dealing with advisories:
The advisories which we receive range in quality / detail.
A personal favourite are the drupal advisories. We offer the drupal core as a package but not any of the 3rd party modules. Their advisories clearly indicate if they apply to core or any published 3rd party modules and which scenario is needed for the vulnerability to be exploitable eg the user must be able to upload content.

The opposite of that is independently published advisories without any co-ordination with affected parties or independently published advisories which are disputed or not acknowledge from upstream. In these situation the role becomes more involved in order to work out if there is clearly an issue or not.

Then there’s Oracle advisories, we can confirm there’s one or more problems in the following versions of software, no more details than that. Upgrade to this version at a minimum to fix said issue(s). Here’s a chart so you can evaluate the risk.

It can be that upstream has actually made an announcement with the details of an issue in public but the mitre website will still lists the CVE as reserved. Ideally you’d like to list the mitre site in pkg-vulnerabilities as it’s where IDs are assigned and it’s self referencing (url will contain the CVE id). But it’s a terrible thing to do to a user. “You have a package installed which is vulnerable to the following type of issue follow this link to not find out any more information about it. Go fish”. Or maybe you have no choice.

Project Websites:
If the published advisory come via a Linux distribution it can be common that the fix references a binary package for users to install or perhaps further information required. In the 2000’s Soureceforge was a popular host for open source projects usually complimented with a separate web page of some kind, it’s now common to have projects which solely exists as an authoritative repo on github. In either scenario, a dedicated section for publishing security information is usually not found. This trend is also prevelant in large commercially backed projects, which play an extremely critical role. Projcts such as ICU (International Components for Unicode), a project by IBM which deals with unicode, an issue in ICU can mean an issue in chrome/chromium, java.

There are also projects like Qemu which have a security page for submitting vulnerability information but never publish advisories themselves. It is common for advisories to reference a git commit email. KVM completely lacks any links related to security. Qemu has a strong link with Xen & KVM which rely on Qemu in one way or another.
While we do not offer KVM as a package, we do at present have four different versions of Xen in our tree and Qemu. This becomes a bit of a timesink when there are multiple advisories to address.

Commercial Repositories:
There are opensource projects with no publicly accessible source code repo. This makes the evaluation of the range of effected verisons difficult if the project only chooses to cover their supported versions.
ISC up until recently (past two years?) required paid membership to access BIND’s repo.
In the talk I refered to the ICU project here, this was incorrect. ICU advisories are either reserved or the bug report access blocked from public view.

OpenSSL:
Relationships with projects are important and they play a critical role in not only sharing information but code as well. Changes for 3rd party software really needs to be passed to the 3rd party to take care of. If relationships have tourned sour, it makes sharing somewhat difficult and has further implications when developing a project with the support for other projects in mind.
The LibreSSL project published a patches page which covered the changes needed to get affected software built but also co-ordinated with upstream projects to get the fixes integrated. Some projects needed more pressure^Wpersuasion than others to accept the patches.

Key components & deadware:
As mentioned previously, you want changes to go back up stream and not to carry changes in your own tree. But there are scenarios where this is possible, for example, the project is no longer developed. This is a huge problem if the project is widely used because you end up carrying local patches which hinders progress when auditing for vulnerabilites by consumers of the software downstream. It’s no longer a case of ensuring you have a specific version number but which patches are also applied to that baseline version, that then opens further questions about the patches, have you created a new issue that didn’t exist previously??
The widely used unzip utility is such an example,  are you patched for CVE-2015-7696?

An example fragmentation of fixes being carried locally is libwmf, with the announcement of some CVEs earlier this year, Jason Unovitch from the FreeBSD project discovered that there were unpatched vulnerabilities in this library going back to 2004, with patches spread across different Linux distributions, none carrying fixes for all advisories, in one case a hunk of the patch didn’t even apply. Development for libwmf stopped in the early 2000’s but it still exists as a project on sourceforge.

Jasper is another commonly used graphics library, this time for jpeg-2000, again development ceased long ago. In this case Slackware put out an advisory for their package to cover vulnerabilities from the past, going back to 2008, at which point we realised that we didn’t have the fixes either. The version in OpenBSD ports was vulnerable to the issues listed from 2014 but the vulnerabilities from prior (2008) were fixed because they’d been flagged up by the compiler in OpenBSD.

Widely Deployed:
Popular projects which have a large install base can greatly increase impact of a mistake, hence local changes should be kept to a minimum to ease maintanence and auditability.
Projects can see a very fast release cycle, especially ones which have advisories published about them regularly.
Keeping local changes to a minimum reduces the necessary effort to update. With projects which rely on downstream consumers to publish information it makes the process more difficult. Both KVM & QEMU projects do not publish any advisories themselves, at best you may have a git commit email which may be the patch you carry locally. Thankfully the Xen project publish advisories on Qemu as it can be a dependency. They are able to flesh out the details of the issue a little better than a vague commit message.
I’m unsure what happens if you’re not a Linux distro and utilise KVM.

Co-ordinating with upstream:
As I mentioned, relationships are important. An understanding and tolerrance for difference is absolutely essential in the world of software just as it is in day to day life. A common topic of disagreement is licensing, the terms expressed by said licenses and the strong opinions expressed by the participants in the disagreement. Whatever ones belief, the need to co-ordinate with people from different groups is absolutely necessary.
Of the fixes upstreamed from LibreSSL, the author of stunnel rejected a fix initially but eventually changed his mind. The change in question was a 2 line addition to add an ifdef statement so that RAND_egd function was only used if the SSL library being linked to offered such a function (detected by autoconf already). The author rejected the change based on terms of licensing of his project when the change was submitted.

Taking bigger leaps in a software project by trying to clean up a popular target can amass a large collection of local patches which need to make their way upstream. As observed by the Alpine Linux project, a Linux distribution with a new libc called musl libc. While it’s possible to build over 13000 packages with Debian 8 on pkgsrc, the package count is less than 9000 on Alpine, despite both being Linux distributions.

The submission process can be quite daunting depending on the project, to filter out submissions which may not be sound and reduce the workload of developers working on a project, some opt to requiring certain things such as results from a test suite or alike. It doesn’t help matters if project has multiple branches developed in parallel without changes being in sync.
Dealing with GNU toochain such as GCC can be very much like this. Again, local changes amass, slow transforming the local version of the toolchain to an extended version of upstream. While the toolchain may offer security features such as SSP (stack smashing protection), it’s not just the simple case of being able to switch it on, in some cases it either doesn’t work or worse, it results in broken binaries. Work to enable some of these features in pkgsrc began in the summer.

While not specifically security related, I was reminded of an incident on the OpenBSD mailing lists with the author of the once popular ion window manager. The ion developer was frustrated with operating system projects packaging older versions of his software with local changes as users where following up with him for support (in this case he was referring to RedHat). So he came on to the OpenBSD mailing list to ask about updating the software to the latest version available but that was not possible due to incompatible license changes. As usual, the combination of making demanding + licensing drama didn’t work out to well.

Conclusion

  • Organise the information on your site, for an Open Source software project your source control repo should be a single click away from your websites main page.
  • Provide a dedicated security page or section where you post advisories.
  • Write descriptive commit messages.
  • Participate in the community and help your neighbours
  • Even if you stop developing software, the code may live on longer than envisioned, think about what happens if/when you decide to stop (who become the authoritative repo).
  • Don’t make changes locally which do not go upstream by default, for it’ll surely bite you or a member of the project later down the line.
  • Publish actual advisories for your project, don’t pass the buck.
  • Technical problems are best solved with technical solutions eg a bug can still continue to exist despite adhering to a license.
  • Make the submission process to your project effortless for both parties, not just one or the other.

One thought on “Adventures in Open Source Software: Dealing with Security

  1. Kyle Amon

    Wisdom. I have long wanted to see some standardization begin to grow in this process (or lack thereof). For those who recall the advisory landscape before MITRE began their CVE project, the potential benefits are obvious. We, as a pluralistic community of Free Software and Open Source enthusiasts of all stripes can certainly do a better job of this. It just needs focus, attention, humility and goodwill. As always, the trouble with security is significantly more anthropic then technical.

    ++

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