CVE-2026-54567 Flask-Reuploaded: Extension-denylist bypass via case-folding asymmetry in name-override path (incomplete-fix variant of CVE-2026-27641)

Flask-Reuploaded provides file uploads for Flask. From 1.5.0 until 1.6.0, UploadSet.savestorage, name=... in src/flaskuploads/flaskuploads.py applies lowercaseext to the default upload path but uses the case-preserving extension helper for a caller-supplied name before extensionallowed evaluates ...