CVE-2026-53600

## Summary `async-tar` v0.6.0 mis-applies a buffered PAX `size` extension to an intermediary extension header (a GNU longname `L`, a GNU longlink `K`, or a PAX `x`/`g` header) instead of to the next *file* entry. POSIX requires a PAX extended-header record set to describe the next file entry, never an intervening extension header. Because `poll_next_raw` (`src/archive.rs`) threads the buffered PAX records into the size computation of whatever raw header it reads next — and that header can be an intermediary `L` — the stream cursor is advanced by an attacker-chosen amount when the `L` body is consumed. The parser then desyncs relative to a POSIX-correct tar parser (e.g. GNU tar), reading subsequent bytes at the wrong block boundary. An attacker who can influence a tar stream that an `async-tar` consumer extracts can construct an `x → L → file` sequence whose entry list and on-disk result differ between `async-tar` and a reference parser. This enables content/entry smuggling: a file that a GNU-tar-based scanner/validator/AV sees as benign opaque data is extracted by `async-tar` as a different file with different bytes (e.g. an executable script), and vice versa. Type confusion / improper validation of the specified quantity (size). CWE-20, CWE-843. Severity assessed Medium, consistent with the same defect class in the upstream tar-rs / tokio-tar lineage. ## Affected code Package: `async-tar` (crates.io). Affected version: **0.6.0** (latest release) and current `main` HEAD. Both lack the extension-header guard. `src/archive.rs`, `poll_next_raw` (line numbers from the v0.6.0 tag, commit `45814b19295b7398e119c90c57d8c8bf70a798b6`): ```rust let file_pos = *next; let mut header = current_header.take().unwrap(); // when pax extensions are available, the size should come from there. let mut size = header.entry_size()?; // the size above will be overriden by the pax data if it has a size field. // same for uid and gid, which will be overridde