High [CVE-2026-39246] arbitrary symlink creation during archive extraction leads to information disclosure

decompress before 4.2.2 allows arbitrary symlink creation during archive extraction. When processing symlink entries (type === 'symlink'), the x.linkname field from the archive is passed directly to fs.symlink() without validation (index.js line 121).

The preventWritingThroughSymlink check on line 98 only applies to file entries, not symlink creation. An attacker can craft an archive with symlink entries pointing to sensitive files outside the extraction directory (e.g., /etc/passwd), enabling information disclosure when the application reads the extracted contents.

A flaw was found in the decompress package for Node.js. The package creates symlinks from archive entries during extraction without validating the link target against the output directory, because the existing containment check only applies to regular file entries.

An attacker who can supply a crafted archive for extraction (for example a malicious package tarball or user-uploaded archive) can create a symlink inside the output directory that points to an arbitrary path such as /etc/passwd.

If the extracting application subsequently reads or serves the extracted files, the attacker can achieve disclosure of any file readable by the extracting process, and in combination with a later write to the same symlinked path, potentially write through the link as well.