How severe is CVE-2026-27641?

CVE-2026-27641 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-27641?

CVE-2026-27641 affects the following packages: flask-reuploaded (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-27641?

Update flask-reuploaded to 1.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27641 is resolved across your whole dependency graph.

How do I detect CVE-2026-27641 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for flask-reuploaded, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-27641 if there is no patch (or I can't update yet)?

Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Is CVE-2026-27641 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-27641 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-27641?

CVE-2026-27641 has an EPSS (Exploit Prediction Scoring System) score of 1.3%, placing it in the 71th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-27641?

CVE-2026-27641 is classified as CWE-1336 (CWE-1336), Path Traversal (CWE-22). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-27641 published, and has it been updated?

CVE-2026-27641 was published on February 25, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

CRITICAL severity

CVE-2026-27641 — flask-reuploaded

CRITICALFix: jugmac00/flask-reuploaded@d64c6b2

CVE-2026-27641 is a critical-severity (CVSS 9.8) CWE-1336 vulnerability in flask-reuploaded. A fix is available for flask-reuploaded — see the affected versions and patch details below.

Flask-Reuploaded vulnerable to Remote Code Execution via Server-Side Template Injection

Also known asGHSA-65mp-fq8v-56jrPYSEC-2026-341

Published

Feb 25, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27641.

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs71th percentile — riskier than 71% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍flask-reuploaded

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

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).

Patches

Flask-Reuploaded has been patched in version 1.5.0

Workarounds

Do not pass user input to the name parameter
Use auto-generated filenames only
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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`flask-reuploaded`	all versions	1.5.0`pip install --upgrade 'flask-reuploaded==1.5.0'`

Affected Products

1 product · 1 configurations

Application

flask-reuploadedjugmac00

< 1.5.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for flask-reuploaded, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update flask-reuploaded to 1.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27641 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

### Impact 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). ### Patches Flask-Reuploaded has been patched in version 1.5.0 ### 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 ```python from werkzeug.utils import secure_filename import os # Sanitize user input before passing to save() safe_name = secure_filename(reques