AIKIDO-2026-386051

TL;DR

The filesystem extraction API in modern-tar creates symlinks, hardlinks, and files from archive entries while validating link targets only lexically at creation time. Extracting a crafted archive can redirect writes outside the destination directory through unvalidated hardlinks, symlink chains, parent-directory races, or pre-existing link leaves, allowing files to be overwritten beyond the extraction root. Oversized or malformed PAX and metadata entries can also stall parsing and consume excessive resources during extraction. The fix validates the full symlink graph against the resolved destination after extraction, rejects parent swaps and excessive symlink following, opens destination files with O_EXCL, and caps and hardens PAX and metadata parsing.