The SolarWinds attack brought additional scrutiny software supply chain security, but concerns about organizations’ software supply chains have been discussed for a number of years. Development organizations’ shift to DevOps or DevSecOps has pushed teams to adopt new technologies in the build pipeline – often hosted by 3rd parties. This has resulted in build pipelines that expose a complicated and often uncharted attack surface. In addition, modern products also incorporate code from a variety of contributors – ranging from in-house developers, 3rd party development contractors, as well as an array open source contributors. This talk looks at the challenge of developing secure build pipelines. This is done via the construction of a threat model for an example software build pipeline that walks through how the various systems and communications along the way can potentially be misused by malicious actors. Coverage of the major components of a build pipeline – source control, open source component management, software builds, automated testing, and packaging for distribution – is used to enumerate likely attack surface exposed via the build process and to highlight potential controls that can be put in place to harden the pipeline against attacks. The presentation is intended to be useful both for evaluating internal build processes as well as to support the evaluation of critical external vendors’ processes.