Secure Software doesn't develop itself.

The picture shows the top layer of the Linux kernel's API subsystems. Source: https://www.linux.org/attachments/kernel-jpeg.6497/

Category: Development

Continuous Integration is no excuse for a complex Build System

The picture shows a computer screen with keyboard in cartoon style. The screen shows a diagram of code flows with red squares as a marker for errors.Continuous Integration (CI) is a standard in software development. A lot of companies use it for their development process. It basically means using automation tools to test new code more frequently. Instead of continuous, you can also use the word automated, because CI can’t work manually. Modern build systems comprise scripts and descriptive configurations that invoke components of the toolchain in order to produce executable code. Applications build with different programming languages can invoke a lot of tools with individual configurations. The build system is also a part of the code development process. What does this mean for CI in terms of secure coding?

First, if you use CI methods in your development cycle, then make sure you understand the build system. When working with external consultants that audit your code, the review must be possible without the CI pipeline. In theory, this is always the case, but I have seen code collections that cannot be built easily, because of the many configuration parameters hidden in hundreds of directories. Some configuration is old and use environment variables to control how the toolchain has to translate the source. Especially cross-platform code is difficult to analyse because of the mixture of tools. Often it is only possible to study the source. This is a problem, because a code review also needs to rebuild the code with changing parameters (for example, changing compiler flags, replacing compilers, adding analyzers, etc.). If the build process doesn’t allow this, then you have a problem. This makes switching to different tools impossible, which is also necessary when you need to test new versions of your programming language or need to migrate old parts of your code to a newer standard.

Furthermore, if your code cannot be built outside your CI pipeline, then reviews are basically impossible. Just reading the source means that a lot of testing cannot be done. Ensure that your build systems do not grow into a complex creation no one wants to touch any more. The rules of secure and clean coding also apply to your CI pipeline. Create individual packages. Divide the build into modules, so that you can assemble the final application from independent building blocks. Also, refactor your build configuration. Make is simpler and remove all workarounds. Once the review gets stuck and auditors have to read your code like the newspaper, it is too late.

Using AI Language Models for Code Creation

The picture show the inside of a circuit box created by the Midjourney AI graphic generation algorithm.The trend of large language models (LLMs) continues. Many people are doing experiments and explore how these algorithms can help them when developing software. Most integrated development environments have features that help you while writing code. Access to documentation, function call parameters, static checks, and suggestions are standard tools to help you. LLMs are the new kid on the block. Some articles describe how questions (or prompts) to chat engines were used to create code samples. The output depends a lot on the prompt. Changing words or rephrasing the prompt can lead to different results. This differs from the way other tools work. Getting useful results means to play with the prompt and engage in trial-and-error cycles. Algorithms such as ChatGPT are not sentient. They cannot think. The algorithm just remixes and repeats part of its training data. Asking for code examples is probably most useful for getting templates or single functions. This use case is disappointingly close to browsing tutorials or Stackoverflow.

Designing prompts is a new skill artificially created by LLMs algorithms. This is another problem, because you now need to collect prompts for creating the most useful code. The work shifts to another domain, but you don’t actually save time unless you have a compendium of prompts. Creating useful and well-tested templates is a better use of resources. The correct of of patterns governs code creating with or without LLMs.

The security questions have not been addressed yet. There are studies that analyse how the code quality of tool- and human-generated code looks like. According to the Open Source Security and Risk Analysis (OSSRA) report from 2022, the code created by assistant features contained vulnerabilities 40% of the time. An examination of code created by Github’s Copilot shows that autogenerated code contains bugs that belong to specific software weaknesses. The code created by humans has a distinct pattern of weaknesses. A more detailed analysis can only be done by larger statistical samples, because Copilot’s training data is proprietary and not accessible. There is room for more research, but it is safe to say that LLMs also make mistakes. Output from these algorithms must be included in the quality assurance cycle, with no exceptions. Code generators cannot work magic.

If you are interested in using LLMs for code creation, make sure that you understand the implications. Developing safe and useful templates is a better way than to engineer prompts for the best code output. Furthermore, the output can change whenever the LLM changes its version or training data. Using algorithms to create code is not a novel approach. Your toolchains most probably already contain code generators. In either case, you absolutely have to understand how they work. This is not something an AI algorithm can replace. The best approach is to study the code suggested by the algorithm, transfer it into pseudo-code, and write the actual code yourself. Avoid cut & paste, otherwise your introduce more bugs to fix later.

Presentation Supply Chain Attacks and Software Manifests

Today I held a presentation about supply chain attacks and software manifests. The content covers my experience with exploring standards for Software Bill of Materials (SBOMs). While most build systems support creating the manifests, the first step is to identify what components you use and where they come from. Typical software projects will use a mixture of sources such as packet managers from programming languages, operating systems, and direct downloads from software repositories. It is important to focus on the components your code directly relies on. Supporting applications that manage a database or host application programming interfaces (APIs) are a requirement, but usually not part of your software.

The presentation can be found by using this link. The slides are in German, but you will find plenty of links to sources in English.

Creating Software Bill of Materials (SBOM) for your Code

All software comprises components. Given the prevalence of supply chain attacks against modules and libraries, it is important to know what parts your code uses. This is where the Software Bill of Materials (SBOM) comes into play. A SBOM is a list of all components your code relies on. So much for the theory, because what is a component? Do you count all the header files of C/C++ as individual components or just as parts of the library? Is it just the run-time environment or do you also list the moving parts you used to create the final application? The latter includes all tools working in intermediate processes. A good choice is to focus on the application in its deployment state.

How do you get all the components used in the run-time version of your application? The build process is the first source you need to query. The details depend on the build tool you use. You need to extract the version, the source of the packaged component (this can be a link on the download source or a package URL), the name of of component, and hashes of either the files or the component itself. If you inspect the CycloneDX or SPDX specifications, then you will find that there are a lot more data fields specified. You can group components, name authors, add a description, complex distributions processes, generic properties, and more details. The build systems and package managers do not provide easy access to all information. The complete view requires using the original source for the component, the operating system, and external data sources (for example, the CPE or links to published vulnerabilities). Don’t get distracted by the sheer amount of information that can be included in your manifest. Focus on the relevant and easy to get data about your components.

Hashes of your components are important. When focussing on the run-time of your application, make sure you identify all parts of it. To give an example of C/C++ code, you can identify all libraries your applications load dynamically. Then calculate the hashes of the libraries on the target platform. SBOMs can be different for various target platforms. If you use containers, then you can fix the components. Linking dynamically against libraries means that your code will use different incarnations on different systems. Make sure that you calculate more than one hash for your manifest. MD5 and SHA-1 are legacy algorithms. Do not use them. Instead, use SHA-2 with 256 bit or more and one hash of the SHA-3 family. This guards against hash collisions, because SHA-3 is not prone to content appending attacks.

Software Bill of Materials (SBOM)

No software projects can do without components. Software libraries are the most common ingredient. Some programming languages use the concept of modules or plugins. Then there are frameworks typically used in web applications. All of these parts can feature different versions, because some requirement fixed the version to a major release. If one component exhibits a security vulnerability, then the code in question must be updated. Given the size of modern applications, this can be a challenge. Remember the Log4j vulnerability from last year. Many teams didn’t even know that they were running applications containing Log4j. Attackers know about this and target the supply chain of the code. Finding a critical bug in components can open up a wide variety of code for attacks. This is where the Software Bill of Materials (SBOM) comes into play.

SBOM is simply a list of components that your applications contains. Most teams using build tools have this already implicitly. Basically, SBOM is a standard for the manifest of components your software brings with it. The National Telecommunications and Information Administration (NTIA) has compiled a set of resources describing how to use the standard. The idea is not new. There already exists Software Package Data Exchange® (SPDX®), OWASP CycloneDX, and ISO/IEC 19770-2:2015. Everything boils down to a specification for a JSON document that contains all relevant metadata of all components. The key is to catch all the dependencies. Some libraries depend on others, so package managers can resolve these links and install additional components. Build systems do this automatically, but the SBOM needs to be complete. Another problem is the categorisation. Some parts of the code belong to the runtime, some are managed by the operating system, and others are shipped within the application itself. A full SBOM needs to combine these sources. Your toolchain can help you there. C/C++ compiler can create a list of all headers used during compilation (the Clang/GCC flags -MD and -MF name.out.d take care of it). This is just a part of the development environment. You have to create a manifest for container images and other deployment methods as well. Be as accurate as possible, and make sure that SBOM creating is an automated part of your build pipeline.

Powered by WordPress & Theme by Anders Norén