Package Instance

Decidim's private data exports can lead to data leaks
Private data exports can lead to data leaks in cases where the UUID generation causes collisions for the generated UUIDs.

The bug was introduced by #13571 and affects Decidim versions 0.30.0 or newer (currently 2025-09-23).

This issue  was discovered by running the following spec several times in a row, as it can randomly fail due to this bug:

```bash
$ cd decidim-core
$ for i in {1..10}; do bundle exec rspec spec/jobs/decidim/download_your_data_export_job_spec.rb -e "deletes the" || break ; done
```

Run the spec as many times as needed to hit a UUID that converts to `0` through `.to_i`.

The UUID to zero conversion does not cause a security issue but the security issue is demonstrated with the following example.

The following code regenerates the issue by assigning a predefined UUID that will generate a collision (example assumes there are already two existing users in the system):

```ruby

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Decidim is a participatory democracy framework. Starting in version 0.27.0 and prior to versions 0.27.5 and 0.28.0, the dynamic file upload feature is subject to potential cross-site scripting attacks in case the attacker manages to modify the file names of the records being uploaded to the server. This appears in sections where the user controls the file upload dialogs themselves and has the technical knowledge to change the file names through the dynamic upload endpoint. Therefore I believe it would require the attacker to control the whole session of the particular user but in any case, this needs to be fixed. Successful exploit of this vulnerability would require the user to have successfully uploaded a file blob to the server with a malicious file name and then have the possibility to direct the other user to the edit page of the record where the attachment is attached. The users are able to craft the direct upload requests themselves controlling the file name that gets stored to the database. The attacker is able to change the filename e.g. to `<svg onload=alert('XSS')>` if they know how to craft these requests themselves. And then enter the returned blob ID to the form inputs manually by modifying the edit page source. Versions 0.27.5 and 0.28.0 contain a patch for this issue. As a workaround, disable dynamic uploads for the instance, e.g. from proposals.

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Decidim is a participatory democracy framework, written in Ruby on Rails, originally developed for the Barcelona City government online and offline participation website. The external link feature is susceptible to cross-site scripting. This allows a remote attacker to execute JavaScript code in the context of a currently logged-in user. An attacker could use this vulnerability to make other users endorse or support proposals they have no intention of supporting or endorsing. The problem was patched in versions 0.27.3 and 0.26.7.

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Decidim is a participatory democracy framework, written in Ruby on Rails, originally developed for the Barcelona City government online and offline participation website. The processes filter feature is susceptible to Cross-site scripting. This allows a remote attacker to execute JavaScript code in the context of a currently logged-in user. An attacker could use this vulnerability to make other users endorse or support proposals they have no intention of supporting or endorsing. The problem was patched in version 0.27.3 and 0.26.7.

Operation on a Resource after Expiration or Release
Decidim is a participatory democracy framework. Starting in version 0.4.rc3 and prior to version 2.0.9 of the `devise_invitable` gem, the invites feature allows users to accept the invitation for an unlimited amount of time through the password reset functionality. This issue creates vulnerable dependencies starting in version 0.0.1.alpha3 and prior to versions 0.26.9, 0.27.5, and 0.28.0 of the `decidim,` `decidim-admin`, and `decidim-system` gems. When using the password reset functionality, the `devise_invitable` gem always accepts the pending invitation if the user has been invited. The only check done is if the user has been invited but the code does not ensure that the pending invitation is still valid as defined by the `invite_for` expiry period. Decidim sets this configuration to `2.weeks` so this configuration should be respected. The bug is in the `devise_invitable` gem and should be fixed there and the dependency should be upgraded in Decidim once the fix becomes available. `devise_invitable` to version `2.0.9` and above fix this issue. Versions 0.26.9, 0.27.5, and 0.28.0 of the `decidim,` `decidim-admin`, and `decidim-system` gems contain this fix. As a workaround, invitations can be cancelled directly from the database.

Decidim has broken access control in templates
### Impact

The `templates` module does not enforce the correct permissions, allowing any logged-in user to access to this functionality in the administration panel. An attacker could use this vulnerability to change, create or delete templates of surveys.

Exposure of Sensitive Information to an Unauthorized Actor
Decidim is a participatory democracy framework, written in Ruby on Rails, originally developed for the Barcelona City government online and offline participation website. Decidim uses a third-party library named Ransack for filtering certain database collections (e.g., public meetings). By default, this library allows filtering on all data attributes and associations. This allows an unauthenticated remote attacker to exfiltrate non-public data from the underlying database of a Decidim instance (e.g., exfiltrating data from the user table). This issue may lead to Sensitive Data Disclosure. The problem was patched in version 0.27.3.

Race condition in Endorsements
A race condition in the endorsement of resources (for instance, a proposal) allows a user to make more than once endorsement.

To exploit this vulnerability, the request to set an endorsement must be sent several times in parallel.