Google Launches OSS Rebuild

Google has announced OSS Rebuild, a new project designed to detect supply chain attacks in open source software by independently reproducing and verifying package builds across major repositories. The initiative, unveiled by the company's Open Source Security Team, targets PyPI (Python), npm (JavaScript/TypeScript), and Crates.io (Rust) packages.

The system, the company said, automatically creates standardized build environments to rebuild packages and compare them against published versions. OSS Rebuild generates SLSA Provenance attestations for thousands of packages, meeting SLSA Build Level 3 requirements without requiring publisher intervention. The project can identify three classes of compromise: unsubmitted source code not present in public repositories, build environment tampering, and sophisticated backdoors that exhibit unusual execution patterns during builds.

Google cited recent real-world attacks including solana/webjs (2024), tj-actions/changed-files (2025), and xz-utils (2024) as examples of threats the system addresses. Open source components now account for 77% of modern applications with an estimated value exceeding $12 trillion. The project builds on Google's hosted infrastructure model previously used for OSS Fuzz memory issue detection.

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