GHSA-jcjr-rh8q-7xqf

In target-directory forms (`ln SOURCE... DIRECTORY`), `ln` rejects source paths with non-UTF-8 filename bytes, while GNU accepts them. Breaks GNU compatibility for byte-oriented filenames on Unix filesystems.

PoC: ``` name=$(printf 'bad_\377'); mkdir dst; : > "$name"; ln "$name" dst # GNU: exit 0, creates dst/bad_\377 ; uutils: exit 1, dst empty ```

--- _Zellic private finding (zellic-ext/coreutils-private PR #84). Reported in the Zellic *uutils coreutils Program Security Assessment* (for Canonical, Jan 2026), audited commit `3a07ffc5a9bd4c283e75afa548ba1f1957bad242`._