# CVE-2011-4137: Django URLField denial of service via uncontrolled URL access

Source: https://junglewise.ai/threats/cve-2011-4137-django-urlfield-denial-of-service-via-uncontrolled-url-access  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2011-10-19. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2011-4137 · Severity: low · CVSS 3.1 · Published 2011-10-19

Django's URLField validator used to verify URLs by making network requests without timeout controls, allowing attackers to cause server resource exhaustion (denial of service) by providing URLs that respond slowly, hang indefinitely, or send large amounts of data. This vulnerability affects web applications that rely on Django's URL validation with the verify_exists option enabled.

Technologies: [Django (PyPI)](https://junglewise.ai/threats/technologies/django). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2011-4137 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2011-4137 being exploited in the wild.

**How severe is CVE-2011-4137?** Low severity, with a CVSS score of 3.1, published 19 October 2011.

**Which products and versions are affected?** Django (PyPI) ECOSYSTEM:introduced=0,fixed=1.2.7, ECOSYSTEM:introduced=0,fixed=1.2.7,introduced=1.3,fixed=1.3.1.

**Is there a fix for CVE-2011-4137?** Yes. Django (PyPI): upgrade to 1.2.7, 1.3.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2011-4137 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2011-4137?** Check whether you run Django (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Django (PyPI): upgrade to 1.2.7, 1.3.1 or later

  ```sh
  pip install "Django>=1.3.1"
  ```


## Technical details

The vulnerability exists in Django's URLField validator verify_exists functionality, which attempted to verify URLs by making HTTP requests using Python's urllib2 library without imposing timeout constraints. An attacker can exploit this by submitting specially crafted URLs that respond very slowly, maintain open connections without sending data, or return extremely large responses, causing the Django process to consume resources and become unresponsive. The vulnerability affects Django versions before 1.2.7 and 1.3.x before 1.3.1. The fix removes the verify_exists functionality entirely, replacing it with safer URL validation that does not make network requests.

## Affected products

- Django Django before 1.2.7 and 1.3.x before 1.3.1

## Identifiers

- CVE-2011-4137
- GHSA-3jqw-crqj-w8qw
- PYSEC-2011-2

## Timeline

- 2011-09-09: disclosed
- 2011-09-10: patched
- 2018-07-23: advisory

## References

- [https://github.com/django/django/commit/1a76dbefdfc60e2d5954c0ba614c3d054ba9c3f0](https://github.com/django/django/commit/1a76dbefdfc60e2d5954c0ba614c3d054ba9c3f0)

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