CVE-2025-27399: mastodon Information Disclosure — Fix

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.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Weakness Type (CWE)

CWE-200 CWE-200

CWE-285 CWE-285

Affected Products

Vendor	Product	Versions
joinmastodon	mastodon	< 4.1.23
joinmastodon	mastodon	4.2.0 — 4.2.16
joinmastodon	mastodon	4.3.0 — 4.3.4

References

Advisories & Patches

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

Other References

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 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. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2025-27399? +

CVE-2025-27399 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-27399? +

CVE-2025-27399 affects products from joinmastodon, specifically: mastodon. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-27399? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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