CVE-2026-54567 Flask-Reuploaded: Extension-denylist bypass via case-folding asymmetry in name-override path (incomplete-fix variant of CVE-2026-27641)
Attackers can bypass extension denylists via case-folding flaws to upload executable files, leading to remote code execution on affected Flask deployments.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54567?
CVE-2026-54567 is a high-severity vulnerability in jugmac00 flask-reuploaded, published on 14 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-54567?
3 open source packages ship an affected version, including flask-reuploaded and Flask-Reuploaded.
| Package | Affected | Fixed in |
|---|---|---|
flask-reuploaded PyPI | All versions | 1.6.0 |
flask-reuploaded PyPI | All versions | 1.6.0 |
Flask-Reuploaded PyPI | All versions | 1.6.0 |
How do I fix CVE-2026-54567?
Upgrade flask-reuploaded to 1.6.0 or later.
Is CVE-2026-54567 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54567 exists.
Sources
Also known as GHSA-937x-gpqr-72gg, PYSEC-2026-3466.