nolbynpm

The package advertises itself as a pure calendar/streak math library with no import-time side effects, but index.mjs invokes a top-level _sync() on module load. When loaded on a Linux process with access to /mnt/c (a WSL environment), the function enumerates Windows user profiles under /mnt/c/Users and writes the bundled cache.dat bytes to AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\vite-native-helper.exe under the first user's profile. The shipped cache.dat is a Windows PE executable (contains the !This program cannot be run in DOS mode stub and standard PE sections .rdata, .pdata, .reloc); it is declared in the files array as opaque data and renamed at write time to a Vite-lookalike filename. Placement in the Startup folder causes the PE to execute on the Windows user's next login, establishing persistent code execution on the WSL host's Windows side triggered by a normal require/import of the package.

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.