Visibility Flaw in Mastodon Microblogging Platform Allows Unauthorized Access to Block Reasons
CVE-2025-27399
5.3MEDIUM
What is CVE-2025-27399?
Mastodon, a popular self-hosted microblogging platform, has a visibility exposure issue affecting versions before 4.1.23, 4.2.16, and 4.3.4. In instances where the visibility setting for domain blocks is configured to display reasons to logged-in users, unapproved users are still able to see these block reasons. This poses a significant privacy risk for instance administrators who wish to keep block reasons confidential. Upgrading to the specified versions will mitigate this issue and enhance user privacy on the platform.
Affected Version(s)
mastodon < 4.1.23 < 4.1.23
mastodon >= 4.2.0, < 4.2.16 < 4.2.0, 4.2.16
mastodon >= 4.3.0, < 4.3.4 < 4.3.0, 4.3.4