# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Sep 2026
- **Updated:** 16 Sep 2026
- **Also known as:** GHSA-937x-gpqr-72gg, PYSEC-2026-3466

## 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.

Weakness: CWE-434 (Unrestricted Upload of File with Dangerous Type), CWE-178 (Improper Handling of Case Sensitivity)

## Which versions are affected by CVE-2026-54567?

3 open source packages ship an affected version, including flask-reuploaded and Flask-Reuploaded.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54567 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54567 exists.

Affected packages and fixed versions:
- flask-reuploaded (PyPI): affected all versions; fixed in 1.6.0
- flask-reuploaded (PyPI): affected all versions; fixed in 1.6.0
- Flask-Reuploaded (PyPI): affected all versions; fixed in 1.6.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54567/ (Markdown: https://insights.sbomify.com/CVE-2026-54567/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54567
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54567
- OSV: https://osv.dev/vulnerability/CVE-2026-54567

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54567/
Summaries are generated and may contain mistakes; the official description above is the record.