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Drupal file upload by anonymous or untrusted users into public file systems — PSA-2016-003

October 10th, 2016

Description

Recently the Drupal Security Team has seen a trend of attacks utilizing a site mis-configuration. This issue only affects sites that allow file uploads by non-trusted or anonymous visitors, and stores those uploads in a public file system. These files are publically accessible allowing attackers to point search engines and people directly to them on the site. The majority of the reports are based around the webform module, however, other modules are vulnerable to this misconfiguration as well. For example, if a webform configured to allow anonymous visitors to upload an image into the public file system, that image would then be accessible by anyone on the internet. The site could be used by an attacker to host images and other files that the legitimate site maintainers would not want made publicly available through their site.

To resolve this issue:

  1. Configure upload fields that non-trusted visitors, including anonymous visitors, can upload files with, to utilize use the private file system.
  2. Ensure cron is properly running on the site. Read about setting up cron for for Drupal 7 or or Drupal 8).
  3. Consider forcing users to create accounts before submitting content.
  4. Audit your public file space to make sure that files that are uploaded there are valid.

Awareness acknowledgment

The Drupal Security Team became aware of the existence and exploits of this issue because the community reported this issue to the security team. As always, if your site has been exploited, even if the cause is a mistake in configuration, the security team is interested in hearing about the nature of the issue. We use these reports to look for trends and broader solutions.

Coordinated by

This post may be updated as more information is learned.

Contact and More Information

The Drupal security team can be reached at security at drupal.org or via the contact form at https://www.drupal.org/contact. Learn more about the Drupal Security team and their policies, writing secure code for Drupal, and securing your site.