Can curl avoid to be in a future funnily named exploit that shakes the world?

During this year we’ve seen heartbleed and shellshock strike (and a  few more big flaws that I’ll skip for now). Two really eye opening recent vulnerabilities in projects with many similarities:

  1. Popular corner stones of open source stacks and internet servers
  2. Mostly run and maintained by volunteers
  3. Mature projects that have been around since “forever”
  4. Projects believed to be fairly stable and relatively trustworthy by now
  5. A myriad of features, switches and code that build on many platforms, with some parts of code only running on a rare few
  6. Written in C in a portable style

Does it sound like the curl project to you too? It does to me. Sure, this description also matches a slew of other projects but I lead the curl development so let me stay here and focus on this project.

cURLAre we in jeopardy? I honestly don’t know, but I want to explain what we do in our project in order to minimize the risk and maximize our ability to find problems on our own before they become serious attack vectors somewhere!

previous flaws

There’s no secret that we have let security problems slip through at times. We’re right now working toward our 143rd release during our around 16 years of life-time. We have found and announced 28 security problems over the years. Looking at these found problems, it is clear that very few security problems are discovered quickly after introduction. Most of them linger around for several years until found and fixed. So, realistically speaking based on history: there are security bugs still in the code, and they have probably been present for a while already.

code reviews and code standards

We try to review all patches from people without push rights in the project. It would probably be a good idea to review all patches before they go in for real, but that just wouldn’t work with the (lack of) man power we have in the project while we at the same time want to develop curl, move it forward and introduce new things and features.

We maintain code standards and formatting to keep code easy to understand and follow. We keep individual commits smallish for easier review now or in the future.

test cases

As simple as it is, we test that the basic stuff works. We don’t and can’t test everything but having test cases for most things give us the confidence to change code when we see problems as we then remain fairly sure things keep working the same way as long as the test go through. In projects with much less test coverage, you become much more conservative with what you dare to change and that also makes you more vulnerable.

We always want more test cases and we want to improve on how we always add test cases when we add new features and ideally we should also add new test cases when we fix bugs so that we know that we don’t introduce any such bug again in the future.

static code analyzes

We regularly scan our code base using static code analyzers. Both clang-analyzer and coverity are good tools, and they help us by pointing out code that look wrong or suspicious. By making sure we have very few or no such flaws left in the code, we minimize the risk. A static code analyzer is better than run-time tools for cases where they can check code flows that are hard to repeat in my local environment.


bike helmetValgrind is an awesome tool to detect memory problems in run-time. Leaks or just stupid uses of memory or related functions. We have our test suite automatically use valgrind when it runs tests in case it is present and it helps us make sure that all situations we test for are also error-free from valgrind’s point of view.


Building and testing curl on a plethora of platforms non-stop is also useful to make sure we don’t depend on behaviors of particular library implementations or non-standard features and more. Testing it all is basically the only way to make sure everything keeps working over the years while we continue to develop and fix bugs. We would course be even better off with more platforms that would test automatically and with more developers keeping an eye on problems that show up there…

code complexity

Arguably, one of the best ways to avoid security flaws and bugs in general, is to keep the source code as simple as possible. Complex functions need to be broken down into smaller functions that are possible to read and understand. A good way to identify functions suitable for fixing is pmccabe,

essential third parties

curl and libcurl are usually built to use a whole bunch of third party libraries in order to perform all the functionality. In order to not have any of those uses turn into a source for trouble we must of course also participate in those projects and help them stay strong and make sure that we use them the proper way that doesn’t lead to any bad side-effects.

You can help!

All this takes time, energy and system resources. Your contributions and help will be appreciated where ever among these tasks that you can insert any. We could do more of all this, more often and more thorough if we only were more people involved!