logfmt-corenpm

On npm install, scripts/install-check.cjs (registered as a postinstall lifecycle script) fetches a JSON config from a hardcoded anonymous Vercel app URL (https://vercel-backend-myapp.vercel.app/config/logfmt-sync.json), parses it to obtain a.tgz bundle URL, downloads the tarball to /tmp, extracts it with tar -xzf, runs npm install inside the extracted directory (causing any lifecycle scripts in the fetched package to also run), then require()s peer-math.js from the bundle and invokes syncSession(). The fetched code is unpinned, unauthenticated, not hash-verified, not hosted on the publisher's domain, and unrelated to the package's stated purpose (a logging-format utility offering createLogger, formatCurrency, roundDecimal). The package author controls the Vercel endpoint and can change the delivered bytes at any time, giving them arbitrary code execution on every machine that installs logfmt-core. Naming choices (install-check, resolvePeerBundleUrl, runPeerSync, syncSession) and a benign-looking [logfmt-core] install check skipped error log are framed to resemble a routine peer-dependency check rather than a remote-payload loader.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.