My submission to the Underhanded C Contest of 2015
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.

Here's my submission for the 2015 Underhanded C Competition.

The vulnerable function is given in match.c; it ostensibly performs a cosine similarity to determine how similar the reference and sample material are.

Can you find the bug?

The underhanded part is in the error checking: as a boundary condition, if the reference AND the sample produce an overflow (i.e. they have really, really big elements), the matching function produces a match. It's the best guess we can make about whether the materials match or not.

The explanation of what goes wrong is in spoiler.c (and the main method shows the bug in action).

This submission got a "runner-up" honorable mention.


The project uses cmake:

git clone
cd underhandedc-2015
mkdir build
cd build
cmake ..

This will generate (hopefully) some sensible files for your build environment. For linux like environments, proceed with:


For Windows, open underhandedc_2015.sln in Visual Studio and compile.

The output should look like this:

Test1 v Reference:     NO_MATCH
Test2 v Reference:     MATCH
Dorked v Reference:    MATCH