Stand on the shoulders of giantsAbout software composition analysis
In our last post,
we reproduced the discovery of
a vulnerability in
But that is only a small library,
you might say,
with a very limited scope
556 KiB installed.
However, many, many packages depend on it.
To see how many packages
in the Arch Linux repository depend on
we can use
by Kylee Keen:
libpngreverse dependencies in
14 GiB worth of software depends on
And that is only in the
Arch Linux repositories,
which is hardly the most popular
Also, the library is the official
PNG reference library and
so certainly many other packages in
other operating systems depend on it.
Now, back in 2015 when
libpng had not yet fixed the low-high palette bug,
all the programs and libraries above
were also automatically vulnerable to the same issue.
Actually this is what happened to
with a vulnerability in
Same with many web services that use
If this could happen to such flagships as
it could happen to your organisation.
In fact, this problem is so common that
it is part of the 2017
OWASP Top 10:
they call it
``A9: Using components with known vulnerabilities''.
Given the rapid adoption of Free and Open Source Software (
by large companies,
all of a sudden dependency vulnerability
appears to be one hell of a problem.
Or rather, as yuppies would like to point out,
a ``business opportunity''?
Many providers of so-called
`software composition analysis'' (`SCA)
(don’t google it)
have since appeared in the security scene.
Some of them are backed by
most are not.
In fact this business has gained such momentum,
that it is expected to grow more than 20% each year
What’s worse, it makes the
that all these companies owe to,
Yet its adoption is not slowing down and,
as we will try to show here,
it’s not its fault but rather,
the dependent app’s;
and also that
it’s not a
FOSS thing but rather
that marketing efforts
point towards it.
Today’s applications use on average
30+ libraries, which represent up to
80% of the code.
Think of it as your code being only
a thin layer upon a building of some
tiny, some larger boxes.
SCA does then is look for
vulnerabilities inside those boxes
with information from external databases,
which then become vulnerabilities in your own app:
SCAscans all the blocks in your app building
Instead of going from the alleged solution towards the source of the problem, let’s do it backwards.
FOSS is developed and used
by thousands around the world.
This can be a double-edged blade:
on the one hand,
according to ``Linus’s Law,''
bug-finding and patching
should be easier as more eyes are involved.
On the other hand, the lack of centralised guiding makes room for bugs. But then again all kinds of software do.
The difference with proprietary software is that, due to all the restrictions it is 'less likely' that their bugs will become public as soon as they would be on the freer side of things. So expect all vulnerabilities to be zero-day.
So if the source of the problem is not
what is it?
The main reasons why so many companies
Not knowing used dependencies.
Ignorance of their vulnerabilities.
No continuous scanning for bugs.
Not testing for compatibility.
In essence, it all boils down to a lack of communication between the user and the source of the components.
So what can you do?
the following guidelines to prevent
Trim unnecessary dependencies, features, components etc. That way you have less to check.
Continuously monitor components for updates and vulnerability reports.
Only obtain components from trusted sources.
Make these guidelines into a company policy.
There are specific tools for this purpose: they compare the version of the dependency you are using against both remote repositories (to check for updates) and vulnerability databases (like to find out if any of your dependencies has reported vulnerabilities that have not been fixed yet.
Note that the language-specific tools
have to be integrated with the
appropriate package manager, like
A bird’s eye view of how the process
should integrate with your development flow is
depicted by the following diagram provided by
SCAin your development flow. Via
We see that every time code is added, the whole system gets scanned for third-party software vulnerabilities and other issues easily identified by Static Analysis when code is not available. This is done by following this procedure:
It is a simple process, really.
Notice that the integration is not fully automatic, and it should not be, since these tools could (and usually do) raise false alarms, so they are reviewed by human security experts.
Internally, the process of scanning for
third party software is the same for both
and it is a simple matter of
querying the vulnerabilities databases
as described above.
Speaking of integration,
you may wonder:
What if my app is deployed inside a container?
`30% of official images in Docker Hub
contain high priority security vulnerabilities'',
according to Pentestit.
Fortunately, there are tools
which go into your container and
perform `SCA inside of it (and more), like
I know you did search for ``Software Composition Analysis'' when I suggested you not to. I just know you did. If you didn’t, good for you! Here’s what you’re missing out on:
All of these industry-leading, award-winning, breakthrough-makers, oracles of the tech future want to sell you one thing: static code analysis plus the tools we discussed above.
While static analysis is a valid tool, it’s just a tool. It can scan code and detect vulnerabilities and unhealthy practices, but also encourages late detection and produces a lot of false positives.
You could try hiring such a service, and maybe even try to complement it with dynamic analysis tools like fuzzing and debuggers, but those have their own issues.
But these are no replacement for good old-fashioned human code review. At least at the moment. According to ,
The only way to deal with the risk of unknown vulnerabilities in libraries is to have someone who understands security analyse the source code. Static analysis of libraries is best thought of as providing hints where security vulnerabilities might be located in the code, not a replacement for experts.
In the future, we might see things like distributed on-demand security testing and machine learning algorithms using support vector machines to try to predict which commits are likely to open vulnerabilities, but in the meantime, stick to the tried-and-true.