Craft CMS has a potential information disclosure vulnerability in preview tokens

Summary

Craft CMS has a CSRF issue in the preview token endpoint at /actions/preview/create-token. The endpoint accepts an attacker-supplied previewToken.

Because the action does not require POST and does not enforce a CSRF token, an attacker can force a logged-in victim editor to mint a preview token chosen by the attacker.

That token can then be used by the attacker (without authentication) to access previewed/unpublished content tied to the victim’s authorized preview scope.

Preconditions

• Victim is logged in to Craft control panel.
• Victim has active preview authorization in session for target content (e.g., opened/edited an entry).
• The attacker must know the target’s canonicalId and public URL path of that entry.

1) Attacker prepares a fixed token

Use any 32-character value, for example:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

2) CSRF victim into minting that token

Send the victim a link (or top-level redirect) such as:

https://TARGET/actions/preview/create-token?elementType=craft%5Celements%5CEntry&canonicalId=123&siteId=1&previewToken=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa&redirect=https%3A%2F%2FTARGET%2F

If the victim is logged in and authorized for previewElement:123, Craft creates that exact token.

3) Attacker accesses preview content unauthenticated

curl -i 'https://TARGET/news/known-entry-slug?token=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'

Expected vulnerable behavior:

• Response renders preview/unpublished state (draft/provisional context), not just normal public content.

Impact

• CSRF-based minting of attacker-known preview tokens.
• Unauthorized access to draft/provisional/revision content via token replay.
• Stealthy one-click exploitation against logged-in editors/admins.
• No dependency on forwarded-host poisoning.