GHSA-3cx6-j9j4-54mp

Impact

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:

$ 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):

# Create the ZIP buffers to be stored
buffer1 = Zip::OutputStream.write_buffer do |out|
  out.put_next_entry("admin.txt")
  out.write "Hello, admin!"
end
buffer1.rewind
buffer2 = Zip::OutputStream.write_buffer do |out|
  out.put_next_entry("user.txt")
  out.write "Hello, user!"
end
buffer2.rewind

# Create the private exports with a predefined IDs
user1 = Decidim::User.find(1)
export = user1.private_exports.build
export.id = "0210ae70-482b-4671-b758-35e13e0097a9"
export.export_type = "download_your_data"
export.file.attach(io: buffer1, filename: "foobar.zip", content_type: "application/zip")
export.expires_at = Decidim.download_your_data_expiry_time.from_now
export.metadata = {}
export.save!


user2 = Decidim::User.find(2)
export = user2.private_exports.build
export.id = "0210d2df-a0c7-40aa-ad97-2dae5083e3b8"
export.export_type = "download_your_data"
export.file.attach(io: buffer2, filename: "foobar.zip", content_type: "application/zip")
export.expires_at = Decidim.download_your_data_expiry_time.from_now
export.metadata = {}
export.save!

Expect to see an...