nvm install --offline installs a cached tarball that previously failed checksum verification

Node Version Manager (nvm) is a POSIX-compliant shell function for managing multiple node.js versions. In versions 0.40.5 through 0.40.8, `nvm_download_artifact` downloads a release archive directly to its final path in `$NVM_DIR/.cache` and verifies its checksum afterwards; on a checksum mismatch it reports an error but leaves the rejected archive in place. A later `nvm install --offline` of the same version installs that cached file without a checksum, so an archive that was just rejected gets installed and its `node` and `npm` run. This gives code execution to a party who can alter the downloaded tarball (for example a poisoned CDN or cache object) but cannot also forge the `SHASUMS256.txt` beside it, if the victim runs `nvm install --offline` for that version after the visible "Checksums do not match" failure and before any online retry. Version 0.41.0 only puts an archive in the cache once its checksum has passed.