CVE-2025-67500: Joinmastodon Mastodon

Low severity, CVSS 3.7. EPSS: 0.2% chance of exploitation in the next 30 days.

Mastodon is a free, open-source social network server based on ActivityPub. Versions 4.2.27 and prior, 4.3.0-beta.1 through 4.3.14, 4.4.0-beta.1 through 4.4.9, 4.5.0-beta.1 through 4.5.2 have discrepancies in error handling which allow checking whether a given status exists by sending a request with a non-English Accept-Language header. Using this behavior, an attacker who knows the identifier of a particular status they are not allowed to see can confirm whether this status exists or not. This cannot be used to learn the contents of the status or any other property besides its existence. This issue is fixed in versions 4.2.28, 4.3.15, 4.4.10 and 4.5.3.

Affected products

• Joinmastodon Mastodon: before 4.2.28 (fixed in 4.2.28); from 4.3.0, before 4.3.15 (fixed in 4.3.15); from 4.4.0, before 4.4.10 (fixed in 4.4.10); from 4.5.0, before 4.5.3 (fixed in 4.5.3)

Published 2025-12-10. Last modified 2026-06-17.