# GHSA-w2j7-f3c6-g8cw: Flask-Security has an Open Redirect issue
> Attackers can bypass redirect validation to send users to malicious sites via phishing when subdomain redirects are enabled.
- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 23 Jun 2026
## What is GHSA-w2j7-f3c6-g8cw?
GHSA-w2j7-f3c6-g8cw is a vulnerability in Flask-Security, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
### Official description
# Open Redirect in Flask-Security
## Summary
`flask_security.utils.validate_redirect_url()` can allow an attacker-controlled redirect URL when subdomain redirects are enabled.
The bypass uses a backslash inside the URL authority/host:
```text
http://evil.com\.whitelist.com
http://evil.com%5C.whitelist.com
```
Python's `urlsplit()` parses the full authority as `evil.com\.whitelist.com` or `evil.com%5C.whitelist.com`. Because the value ends with `.whitelist.com`, `validate_redirect_url()` accepts it as an allowed subdomain of `whitelist.com`.
This is similar in class to the previous Flask-Security-Too open redirect advisory CVE-2023-49438 / GHSA-672h-6x89-76m5, where crafted redirect URLs bypassed validation through browser URL normalization behavior.
## Affected Configuration
The issue requires subdomain redirects to be enabled:
```python
SERVER_NAME = "whitelist.com"
SECURITY_REDIRECT_ALLOW_SUBDOMAINS = True
```
Tested environment:
```text
Flask-Security: 5.8.0
Flask: 3.1.3
Werkzeug: 3.1.8
```
## Impact
An attacker can craft a URL that passes Flask-Security's redirect validation and produces a `302` response to an attacker-controlled URL-like authority.
This can be used for phishing or other attacks that rely on a trusted application redirecting users to an attacker-controlled destination.
## Proof of Concept
### PoC Flask App
```python
from __future__ import annotations
from importlib.metadata import version
from urllib.parse import urlsplit
from flask import Flask, jsonify, redirect, request
from flask_security.utils import validate_redirect_url
app = Flask(__name__)
app.config.update(
SECRET_KEY="poc-only",
SERVER_NAME="whitelist.com",
SECURITY_REDIRECT_ALLOW_SUBDOMAINS=True,
SECURITY_REDIRECT_BASE_DOMAIN=None,
SECURITY_REDIRECT_ALLOWED_SUBDOMAINS=[],
)
@app.get("/")
def index():
return jsonify(
flask_version=version("Flask"),
configured_server_name=app.config["SERVER_NAME"],
examples=[
r"http://evil.com\.whitelist.com",
"http://evil.com%5C.whitelist.com",
"http://sub.whitelist.com",
"http://sub.not-whitelist.com",
],
)
@app.get("/check")
def check():
next_url = request.args.get("next", "")
parsed = urlsplit(next_url)
return jsonify(
next=next_url,
valid=validate_redirect_url(next_url),
parsed={
"scheme": parsed.scheme,
"netloc": parsed.netloc,
"hostname": parsed.hostname,
"path": parsed.path,
},
)
@app.get("/redir")
def redir():
next_url = request.args.get("next", "")
if not validate_redirect_url(next_url):
return jsonify(error="blocked", next=next_url), 400
return redirect(next_url)
if __name__ == "__main__":
app.run(host="127.0.0.1", port=5000, debug=False)
```
### Steps to Reproduce
Run the PoC with the target project's Flask version:
```bash
.venv/bin/python poc_redirect_app.py
```
The invalid comparison case is correctly blocked:
```bash
http://127.0.0.1:5000/redir?next=http://evil.com
```
Observed result:
Check the validation result:
```bash
http://127.0.0.1:5000/check?next=http://evil.com%5C.whitelist.com
```
Observed result:
## References
- CVE-2023-49438: https://advisories.gitlab.com/pypi/flask-security-too/CVE-2023-49438/
- GHSA-672h-6x89-76m5: https://osv.dev/vulnerability/CVE-2023-49438
- NVD entry for CVE-2023-49438: https://nvd.nist.gov/vuln/detail/CVE-2023-49438
## Which versions are affected by GHSA-w2j7-f3c6-g8cw?
2 open source packages ship an affected version, including Flask-Security and flask-security.
| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `Flask-Security` | PyPI | All versions | 5.8.1 |
| `flask-security` | PyPI | All versions | 5.8.1 |
## How do I fix GHSA-w2j7-f3c6-g8cw?
Upgrade Flask-Security to 5.8.1 or later.
## Is GHSA-w2j7-f3c6-g8cw being exploited?
There is no known exploitation of GHSA-w2j7-f3c6-g8cw in the wild and no public exploit code.
## Fix prompt for AI coding agents
```text
Check this codebase for GHSA-w2j7-f3c6-g8cw and fix it if it is affected.
What it is: GHSA-w2j7-f3c6-g8cw is a vulnerability in Flask-Security, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of GHSA-w2j7-f3c6-g8cw in the wild and no public exploit code.
Affected packages and fixed versions:
- Flask-Security (PyPI): affected all versions; fixed in 5.8.1
- flask-security (PyPI): affected all versions; fixed in 5.8.1
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/GHSA-w2j7-f3c6-g8cw/ (Markdown: https://insights.sbomify.com/GHSA-w2j7-f3c6-g8cw/index.md)
```
## Sources
- OSV: https://osv.dev/vulnerability/GHSA-w2j7-f3c6-g8cw
---
From sbomify Insights: https://insights.sbomify.com/GHSA-w2j7-f3c6-g8cw/
Summaries are generated and may contain mistakes; the official description above is the record.