Summary

When unpacking a tar archive, the tar crate's unpackdir function uses fs::metadata() to check whether a path that already exists is a directory. Because fs::metadata() follows symbolic links, a crafted tarball containing a symlink entry followed by a directory entry with the same name causes the crate to treat the symlink target as a valid existing directory — and subsequently apply chmod to it. This allows an attacker to modify the permissions of arbitrary directories outside the extraction root.

Reproducer

A malicious tarball contains two entries: (1) a symlink foo pointing to an arbitrary external directory, and (2) a directory entry foo/. (or just foo). When unpacked, createdir("foo") fails with EEXIST because the symlink is already on disk. The fs::metadata() check then follows the symlink, sees a directory at the target, and allows processing to continue. The directory entry's mode bits are then applied via chmod, which also follows the symlink — modifying the permissions of the external target directory.

Fix

The fix is very simple, we now use fs::symlinkmetadata() in unpackdir, so symlinks are detected and rejected rather than followed.

Credit

This issue was reported by @xokdvium - thank you!

An issue was discovered in the tar crate before 0.4.36 for Rust. When symlinks are present in a TAR archive, extraction can create arbitrary directories via .. traversal.

Node.js tar module could allow a local attacker to traverse directories on the system, caused by insufficient absolute path sanitization. An attacker could use a specially-crafted tar file containing "dot dot" sequences (/../) to create or overwrite arbitrary files on the system.

Impact

Arbitrary File Creation, Arbitrary File Overwrite, Arbitrary Code Execution

node-tar aims to guarantee that any file whose location would be modified by a symbolic link is not extracted. This is, in part, achieved by ensuring that extracted directories are not symlinks. Additionally, in order to prevent unnecessary stat calls to determine whether a given path is a directory, paths are cached when directories are created.

This logic was insufficient when extracting tar files that contained both a directory and a symlink with the same name as the directory. This order of operations resulted in the directory being created and added to the node-tar directory cache. When a directory is present in the directory cache, subsequent calls to mkdir for that directory are skipped. However, this is also where node-tar checks for symlinks occur.

By first creating a directory, and then replacing that directory with a symlink, it was thus possible to bypass node-tar symlink checks on directories, essentially allowing an untrusted tar file to symlink into an arbitrary location and subsequently extracting arbitrary files into that location, thus allowing arbitrary file creation and overwrite.

This issue was addressed in releases 3.2.3, 4.4.15, 5.0.7 and 6.1.2.

Patches

3.2.3 || 4.4.15 || 5.0.7 || 6.1.2

Workarounds

Users may work around this vulnerability without upgrading by creating a custom filter method which prevents the extraction of symbolic links.

js const tar = require('tar')

tar.x({ file: 'archive.tgz', filter: (file, entry) => { if (entry.type === 'SymbolicLink') { return false } else { return true } } })

Users are encouraged to upgrade to the latest patch versions, rather than attempt to sanitize tar input themselves.

An issue was discovered in the tar crate before 0.4.16 for Rust. Arbitrary file overwrite can occur via a symlink or hardlink in a TAR archive.