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.
CVE ID: CVE-2025-27399
CVSS Base Severity: MEDIUM
CVSS Base Score: 5.3
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Vendor: mastodon
Product: mastodon
EPSS Score: 0.05% (probability of being exploited)
EPSS Percentile: 11.66% (scored less or equal to compared to others)
EPSS Date: 2025-03-28 (when was this score calculated)