CVE-2023-49438 is a medium-severity (CVSS 6.1) Open Redirect vulnerability in flask-security-too. 3 public exploit references exist, so weaponization risk is real. A fix is available for flask-security-too — see the affected versions and patch details below.
Open redirect vulnerability in Flask-Security-Too
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-49438 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
flask-security-tooReal-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
An open redirect vulnerability in the python package Flask-Security-Too <=5.3.2 allows attackers to redirect unsuspecting users to malicious sites via a crafted URL by abusing the ?next parameter on the /login and /register routes.
Flask-Security-Too contains logic to validate that the URL specified within the next parameter is either relative or has the same network location as the requesting URL in an attempt to prevent open redirections. Previously known examples that bypassed the validation logic such as https://example/login?next=\\\\\\github.com were patched in version 4.1.0
However, examples such as https://example/login?next=/\\github.com and https://example/login?next=\\/github.com were discovered due to how web browsers normalize slashes in URLs, which makes the package vulnerable through version <=5.3.2
Additionally, with Werkzeug >=2.1.0 the autocorrect_location_header configuration was changed to False - which means that location headers in redirects are relative by default. Thus, this issue may impact applications that were previously not impacted, if they are using Werkzeug >=2.1.0 as the WSGI layer.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | flask-security-too | all versions | 5.3.3pip install --upgrade 'flask-security-too==5.3.3' |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for flask-security-too, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update flask-security-too to 5.3.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-49438 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-49438 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-49438. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
How to detect CVE-2023-49438
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2023-49438 -u https://target- Template
- Python Flask-Security-Too <=5.3.2 - Open Redirect
- Severity
- medium
- Impact
- Allows attackers to redirect users to arbitrary sites, potentially leading to phishing, data theft, or user session hijacking.
- Remediation
- Upgrade Flask-Security-Too to version 5.3.3 or later to mitigate the open redirect vulnerability.
Template by ProjectDiscovery nuclei-templates (ritikchaddha), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2023-49438 in your dependencies?
O3 Security finds CVE-2023-49438 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.