CVE-2021-32618 Open Redirect Vulnerability
Attackers can redirect users to malicious sites via crafted next parameters if Werkzeug's default header correction is disabled.
- 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
What is CVE-2021-32618?
CVE-2021-32618 is a low-severity vulnerability in Flask-Middleware flask-security, published on 17 May 2021. 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
The Python "Flask-Security-Too" package is used for adding security features to your Flask application. It is an is an independently maintained version of Flask-Security based on the 3.0.0 version of Flask-Security. All versions of Flask-Security-Too allow redirects after many successful views (e.g. /login) by honoring the ?next query param. There is code in FS to validate that the url specified in the next parameter is either relative OR has the same netloc (network location) as the requesting URL. This check utilizes Pythons urlsplit library. However many browsers are very lenient on the kind of URL they accept and 'fill in the blanks' when presented with a possibly incomplete URL. As a concrete example - setting http://login?next=\\\github.com will pass FS's relative URL check however many browsers will gladly convert this to http://github.com. Thus an attacker could send such a link to an unwitting user, using a legitimate site and have it redirect to whatever site they want. This is considered a low severity due to the fact that if Werkzeug is used (which is very common with Flask applications) as the WSGI layer, it by default ALWAYS ensures that the Location header is absolute - thus making this attack vector mute. It is possible for application writers to modify this default behavior by setting the 'autocorrect_location_header=False`.
Weakness: CWE-601
Which versions are affected by CVE-2021-32618?
3 open source packages ship an affected version, including flask-security-too and Flask-Security-Too. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
flask-security-too PyPI | All versions | 4.1.0 |
flask-security-too PyPI | All versions | 4.1.0 |
Flask-Security-Too PyPI | All versions | 4.1.0 |
Products include Flask-Security Project Flask-Security.
How do I fix CVE-2021-32618?
Upgrade flask-security-too to 4.1.0 or later.
Is CVE-2021-32618 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-32618 exists.
Public exploit code: 1 Nuclei template.
Other vulnerabilities in Flask-Middleware flask-security
Sources
Also known as GHSA-6qmf-fj6m-686c, PYSEC-2021-123, UBUNTU-CVE-2021-32618.