CVE-2026-27641

Workarounds

1. Do not pass user input to the name parameter
2. Use auto-generated filenames only
3. Implement strict input validation if name must be used

from werkzeug.utils import secure_filename
import os

# Sanitize user input before passing to save()
safe_name = secure_filename(request.form.get('custom_name'))
# Remove path separators
safe_name = os.path.basename(safe_name)
# Validate extension matches policy
if not photos.extension_allowed(photos.get_extension(safe_name)):
    abort(400)
    
filename = photos.save(file, name=safe_name)

Resources

The fix is documented in the pull request, see https://github.com/jugmac00/flask-reuploaded/pull/180.

A proper write-up was created by the reporter of the vulnerability, Jaron Cabral (https://www.linkedin.com/in/jaron-cabral-751994357/), but is not yet available as of time of this publication.

A critical path traversal and extension bypass vulnerability in Flask-Reuploaded allows remote attackers to achieve arbitrary file write and remote code execution through Server-Side Template Injection (SSTI).

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-27641 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.5.0); upgrading removes the vulnerable code path.

Kodem intelligence

Flask-Reuploaded has been patched in version 1.5.0

1. What is CVE-2026-27641? CVE-2026-27641 is a critical-severity path traversal vulnerability in flask-reuploaded (pip), affecting versions < 1.5.0. It is fixed in 1.5.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-27641? CVE-2026-27641 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of flask-reuploaded are affected by CVE-2026-27641? flask-reuploaded (pip) versions < 1.5.0 is affected.
4. Is there a fix for CVE-2026-27641? Yes. CVE-2026-27641 is fixed in 1.5.0. Upgrade to this version or later.
5. Is CVE-2026-27641 exploitable, and should I be worried? Whether CVE-2026-27641 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-27641 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-27641? Upgrade flask-reuploaded to 1.5.0 or later.