CVE-2026-54567

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

This page contains facts from public vulnerability sources. Check the original advisory before updating.

Flask-Reuploaded provides file uploads for Flask. From 1.5.0 until 1.6.0, UploadSet.save(storage, name=...) in src/flask_uploads/flask_uploads.py applies lowercase_ext to the default upload path but uses the case-preserving extension helper for a caller-supplied name before extension_allowed evaluates an AllExcept denylist. An attacker who controls the name override can use a mixed-case dangerous extension to bypass a lowercase denylist and store the file in the served upload directory. Exploitation requires a denylist configuration, a user-influenced name override, and a deployment that resolves or executes extensions case-insensitively; pure allowlists remain protected and path containment is not bypassed. On an execution-capable upload directory, the stored file can execute with the web server's privileges and affect confidentiality, integrity, and availability. This issue is fixed in version 1.6.0.

CVSS 7.5 · High · EPSS 0.6% · Fix available

Published

2026-09-14T17:15:49.272Z

Updated

2026-09-16T15:22:43.885Z

Stack: python

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