CVE-2026-108976 [HIGH] – GNU Emacs before 31.2 (and TRAMP through 2.8.2) allows OS command injection via a filename

GNU Emacs before 31.2 (and TRAMP through 2.8.2) allows OS command injection via a filename because tramp-user-regexp has an incomplete list of disallowed inputs. NOTE: this issue exists because of an incomplete fix for CVE-2026-79992.