CVE-2026-54567

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.

• CWE-178
• CWE-434

• https://github.com/jugmac00/flask-reuploaded/commit/5ded76092429c6eb8a4af941b14fbde40a38fff4
• https://github.com/jugmac00/flask-reuploaded/pull/186
• https://github.com/jugmac00/flask-reuploaded/security/advisories/GHSA-937x-gpqr-72gg
• https://github.com/jugmac00/flask-reuploaded/security/advisories/GHSA-937x-gpqr-72gg

Published

Sep 14, 2026

Last Modified

Sep 16, 2026

Status

Received

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