Postmortem: TanStack NPM supply-chain compromise

On May 11, 2026, the Mini Shai-Hulud worm compromised 84 npm package artifacts across 42 @tanstack/* packages (as well as @squawk/*, @mistralai/* packages, and others) by chaining a GitHub Actions "Pwn Request," cache poisoning, and OIDC token extraction from runner memory — producing the first npm supply chain attack with valid SLSA Build Level 3 attestations. Here's what happened, what was stolen, and what you need to do right now.

On 2026-05-11, an attacker chained a pull_request_target Pwn Request, GitHub Actions cache poisoning across the fork↔base trust boundary, and OIDC token extraction from runner memory to publish 84 malicious versions across 42 @tanstack/* packages on npm. Full postmortem.

We are actively investigating this security incident and sharing our findings here: www.stepsecurity.io/blog/mini-shai-hulud-is-back-a-self-spreading-supply-chain-attack-hits-the-npm-ecosystem