Basic security steps
Level 1 means the supply chain is documented, there’s infrastructure to generate provenance, and systems are prepared for higher SLSA levels.
SLSA is a set of standards and technical controls you can adopt to improve artifact integrity, and build towards completely resilient systems. It’s not a single tool, but a step-by-step outline to prevent artifacts being tampered with and tampered artifacts from being used, and at the higher levels, hardening up the platforms that make up a supply chain. These requirements are explained below, along with the rest of the essential specifications.
SLSA 101
Supply chain threats
Protecting against key threats
Supply chain attacks are an ever-present threat, exploiting weakpoints to interfere with software. The SLSA framework establishes three trust boundaries encouraging the right standards, attestation and technical controls, so you can harden a system from these threats and risks.
This means automatic capability to analyse artifacts, guarantee the original source code, protect against interference that can happen in the build and distribution processes, isolate any hidden vulnerabilities and knowing with certainty which system components might be affected.
Real world examples
High profile attacks like SolarWinds, Codecov or Linux hypocrite commits exploit the kind of supply chain integrity vulnerabilities which may go unnoticed or be underdeveloped, and quickly become extremely public, disruptive and costly in today’s environment.
Attacks can occur at every link in a typical software supply chain, which puts an extra burden on anyone involved in complex critical systems. SLSA's designed with these examples in mind to make sure they’re common knowledge, and easier to protect against.
How it fits into the security ecosystem
There’s more to security than just protection against tampering. From vulnerability management and fuzzing to testing and developer trust, many of these require solutions where effort’s focused on the source. That’s where SLSA complements your wider security efforts, giving you confidence that the code you run is the code you analyzed.
Security levels
A ladder to the ideal state
SLSA’s requirements look at the three general main areas involved in a software artifact’s creation, and where vulnerabilities target - the build, the source, and the dependencies. As the levels scale up, they show that work’s been done to assure there’s more integrity in each area, which can be helpful in scenario planning.
Build integrity
SLSA starts at the build, the last step before an artifact’s released. This makes sure software’s built from the correct sources and dependencies, and hasn’t been modified. More resilient build integrity means protection from modifying code after source control, compromised build platforms or bypassing CI/CD.
Source integrity
Requirements can then focus on the source. All source code should reflect the intent of the software producer, that code and change history stay available for investigation. More resilient source integrity means better protection from bad code submitted without review or compromised source control systems.
Dependencies
Any other software artifacts fetched during the build process. Once the earlier security checks have been put into place, applying SLSA checks recursively to any dependencies in the system can then be followed up, which helps protect potentially massive attack surfaces against dependency confusion attacks.
After the build
Level 2 shows more trustworthiness in the build, builders are source-aware, and signatures are used to prevent provenance being tampered with.
Back to source
Level 3 shows that a system’s builds are fully trustworthy, build definitions come from the source and a system has more hardened CI.
Across the chain
Level 4 means the build environment is fully accounted for, dependencies are tracked in provenance and insider threats are ruled out.