Triage for HackersPrioritize code auditing via ML
Based upon our last experiment, in this article, I will provide a global vision of how our ML for vulnerability discovery approach should work.
First, what problem would this solve? I am repeating myself here but
when one of our analysts has to audit a new continuous
hacking project, usually all they
get is access to one or more big code repositories. And clients expect
vulnerability reports as soon as possible. We would like our predictor
to sort all the files in these repositories according to the likelihood,
or possibility, that they contain a vulnerability so that the analyst
can prioritize the manual inspection. Ideally, when the analyst is
confronted with a new project, instead of looking at an overview of all
files in a repository or its
git log, they could have a number that
ranks each file in the repo with the probability of it containing code
Figure 1. From a messy git log to a prioritized file breakdown
Next, how should this be done? Many different kinds of machine learning algorithms have been used by the authors we have reviewed here: random forests, deep neural networks, clustering, n-grams. The actual algorithm to be used is one of the variables that we can experiment with. For starters, we used a neural network with a single hidden layer for simplicity. Still, this gave us good results for a first iteration. Regardless of the algorithm to be chosen, all of these must be fed with samples of code labeled with their vulnerability, or in the simplest case, a "yes" for vulnerable and a "no" for the rest. Our algorithm will then proceed to "learn", whether it is pattern identification, anomaly detection or clustering, in the training phase, and be able to work in the prediction phase as described above.
What data should we feed to this algorithm? We need lots of labeled data for such an attempt to work, according to Andrew Ng. But not too much that it would be an obstacle. Fortunately, we have a good amount of code vulnerabilities stored in Integrates. The ones we are interested in are those which point to a particular set of lines of code in a specific repository. We should be able to look up these repositories and extract the relevant pieces of code. We could also extract, at random, some other pieces of code and label them as not vulnerable, thus obtaining a dataset. The flow would be as in this image:
Figure 2. Fetching data from Integrates and repositories
This poses several new challenges:
Integratesand the repositories.
Parsing all the obtained files.
Splitting vulnerable and safe code.
Masking the code so as not to expose it.
But from the data analysis point of view, perhaps the most challenging
aspect is: how do we feed code into an algorithm that expects numerical
values or sets thereof, i.e., vectors from a continuum? We discussed
this a bit in our presentation of the
Python data ecosystem, and in our first
iteration, we opted for breaking up the
code string into tokens and further assigning an integer to each of
these. We thus obtain a proper dataset for machine learning:
Figure 3. Embedding via neural network
Other alternatives we will explore are word embeddings, such as
code2vec, which at the moment are not working for us as
they project each token into a vector, while what we need is to map
functions or even entire classes or files into a single vector. Token
sequences are easily reversible, as seen in the last article, but code
embeddings would not be so easy, thus dealing with the masking issue.
Thus far we have performed these experiments in local machines. However,
this is impractical, for many reasons, one of which is the lack of
computational muscle, in particular of
GPUs, which are pretty much a
requirement for deep neural networks. Amazon Web
Services provides a solution called
Sagemaker you are
given a Jupyter notebook in which you can do
data science to your heart’s content. No fuss about setting up machines,
installing dependencies, everything is ready. Such would be our choice
for training the machines. The output of this training process is a
Python object which can make predictions. As seen in
this can be saved in the Keras
H5 format and
loaded again into a
Python script. An easy way to deploy this model to
make predictions would be on a serverless application on
so that it could be readily accessed by the analysts to deal with new
Hopefully, this cycle would be completed by the analyst manually
detecting, confirming and exploiting —should there be a working
environment— vulnerabilities where the classifier predicted high
likelihood and reporting them back to
Integrates. As the
database fills up again, we should repeat the training cycle with a
prudent frequency, which could be daily, weekly, etc. This is another
hyperparameter to be tuned which would provide more data and feedback to
the machine. That would complete the whole cycle:
Figure 4. ML-aided vulnerability discovery cycle
A lot remains to be done, of course:
Determining the best algorithms for each phase.
Tuning all parameters.
Provisioning the infrastructure.
Choosing the best possible embedding.
Connecting to data sources.
We hope to be able to develop this tool in the next 6 to 8 months, or at
the very least experiment with the possibilities
ML provides to
vulnerability discovery and continue reporting the results here. Stay
tuned for more.