CVE-2025-67500: Mastodon Error Handling Discrepancy Enables Private Status Existence Enumeration

Severity: low (CVSS 3.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-12-10 · updated 2026-10-14
Weakness: CWE-204

Description

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

mastodon: before 4.2.28; from 4.3.0 before 4.3.15; from 4.4.0 before 4.4.10; from 4.5.0 before 4.5.3 — fixed in 4.2.28, 4.3.15, 4.4.10, 4.5.3

How to fix

Upgrade to a fixed version: mastodon 4.2.28, 4.3.15, 4.4.10, 4.5.3. Check the vendor advisory for mitigations.

References

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