CVE-2025-62518: astral-tokio-tar Vulnerable to PAX Header Desynchronization

Versions of astral-tokio-tar prior to 0.5.6 contain a boundary parsing vulnerability that allows attackers to smuggle additional archive entries by exploiting inconsistent PAX/ustar header handling. When processing archives with PAX-extended headers containing size overrides, the parser incorrectly advances stream position based on ustar header size (often zero) instead of the PAX-specified size, causing it to interpret file content as legitimate tar headers.

This vulnerability was disclosed to multiple Rust tar parsers, all derived from the original async-tar fork of tar-rs.