GHSA-vg3j-hpm9-8v5v Craft CMS has a potential information disclosure vulnerability in preview tokens

• Packagist craftcms/cms: >= 4.0.0-RC1, < 4.17.3 → fixed in 4.17.3 • Packagist craftcms/cms: >= 5.0.0-RC1, < 5.9.7 → fixed in 5.9.7

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 That token can then be used by the attacker (without authentication) to access previewed/unpublished content tied to the victim’s authorized preview scope.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: ```text aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ``` 2) CSRF victim into minting that token Send the victim a link (or top-level redirect) such as: ```text 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 ```bash 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``` Expected vulnerable behavior: • Response renders preview/unpublished state (draft/provisional context), not just normal public content.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. ---