CVE-2025-27399

Mastodon's domain blocks & rationales ignore user approval when visibility set as "users"

Description

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.

Category

5.3
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 0.05%
Affected: mastodon mastodon
Published at:
Updated at:

References

Link Tags
https://github.com/mastodon/mastodon/security/advisories/GHSA-94h4-fj37-c825
https://github.com/mastodon/mastodon/commit/6b519cfefa93a923b19d0f20c292c7185f8fd5f5
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

Frequently Asked Questions

What is the severity of CVE-2025-27399?
CVE-2025-27399 has been scored as a medium severity vulnerability.
How to fix CVE-2025-27399?
To fix CVE-2025-27399, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2025-27399 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2025-27399 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-27399?
CVE-2025-27399 affects mastodon mastodon.
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