CVE-2025-27399

Mastodon is a self-hosted, federated microblogging platform. In versions prior to 4.1.23, 4.2.16, and 4.3.4, when the visibility for domain blocks/reasons is set to "users" (localized English string: "To logged-in users"), users that are not yet approved can view the block reasons. Instance admins that do not want their domain blocks to be public are impacted. Versions 4.1.23, 4.2.16, and 4.3.4 fix the issue.

The following products are affected by CVE-2025-27399 vulnerability.

Here, you will find a curated list of external links that provide in-depth information to CVE-2025-27399.

URL	Resource
https://github.com/mastodon/mastodon/blob/93f0427b8a84faf68d5d02cdf9a26f98fae16f2b/app/controllers/api/v1/instances/domain_blocks_controller.rb#L33-L35
https://github.com/mastodon/mastodon/blob/93f0427b8a84faf68d5d02cdf9a26f98fae16f2b/app/controllers/api/v1/instances/domain_blocks_controller.rb#L49-L51
https://github.com/mastodon/mastodon/commit/6b519cfefa93a923b19d0f20c292c7185f8fd5f5
https://github.com/mastodon/mastodon/security/advisories/GHSA-94h4-fj37-c825