nvm use --save and nvm install --save write through a symlinked .nvmrc, overwriting any file the user can write

Overview

Node Version Manager (nvm) is a POSIX-compliant shell function for managing multiple node.js versions. In versions 0.40.0 through 0.40.8, nvm use --save and nvm install --save (or -w) write the resolved version to $PWD/.nvmrc with tee, which follows a symbolic link. A repository that commits .nvmrc as a symlink to a path outside itself (git recreates the link on clone) therefore makes --save truncate any file the user can write, such as a shell startup file or ~/.ssh/authorized_keys, and replace its contents with the version string, or create the target of a dangling link; the link itself is left unchanged, so git status stays clean. The attacker does not control the content written, so this is data loss, not code execution. Version 0.41.0 refuses, with a warning, to write when .nvmrc in the current directory is a symlink, dangling or not, rather than writing through it or replacing it.

Affected

• nvm >= 0.40.0 < 0.41.0

Remediation

Upgrade to nvm 0.41.0 or later.

Workarounds

Until upgrading, check that .nvmrc is not a symlink (ls -l .nvmrc) before running nvm use --save or nvm install --save in an untrusted project directory.