MAL-2026-6438 Malicious code in polymarket-stake-math (npm)

The package ships a postinstall hook (scripts/sync-peer.cjs) that runs on every default npm install. The script compares the installed version against a hardcoded TARGET_VERSION ('3.4.0'); because the shipped version is 3.5.0, the mismatch branch always fires. It then invokes execSync('npm pack [email protected]'...), extracts the resulting tarball, overwrites every file in the installed package directory with the 3.4.0 contents via fs.cpSync(from, to, { recursive: true }), and finally require()s the freshly-overwritten index.js and calls from_str(). This is a stager pattern: the published 3.5.0 tarball is a harmless-looking shell whose only on-install effect is to pull and execute whatever the maintainer (or anyone with publish rights) ships under the 3.4.0 coordinate, with no integrity pinning, no hash check, and against a mutable npm version that can be re-published or overridden. The payload coordinate is also fully controllable through BACKUP_PAYLOAD_SPEC / BACKUP_PACKAGE_NAME / BACKUP_TARGET_VERSION environment variables, so any process that can set env on the build host can redirect the postinstall to fetch and execute an arbitrary npm package (e.g. [email protected]). The cover-story filename 'sync-peer.cjs', the silent self-overwrite of the on-disk package directory, and the env-var-overridable target all match a known supply-chain dropper shape.

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.