NodeBB is Node.js based forum software. Starting in version 2.5.0 and prior to version 2.8.7, due to the use of the object destructuring assignment syntax in the user export code path, combined with a path traversal vulnerability, a specially crafted payload could invoke the user export logic to arbitrarily execute javascript files on the local disk. This issue is patched in version 2.8.7. As a workaround, site maintainers can cherry pick the fix into their codebase to patch the exploit.
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.