Misskey vulnerabilities

Misskey, an open source federated social media platform, has a vulnerability in the JSON-LD signature validation and compaction process that allows spoofed activities to be accepted as valid.

Misskey versions from 2024.5.0 up to 2026.5.4 (pre-patch) contain a vulnerability in the Server Announcements API where insufficient permission checks allow attackers to access limited portions of data they normally couldn't view. This vulnerability occurs whether or not federation is enabled.

Misskey, an open-source federated social media platform, versions 12.37.0 through 2026.5.4, is vulnerable to timing attacks during JSON-LD signature validation and compaction. Lack of shared JSON-LD parsing context between signature verification and processing leads to a TOCTOU flaw, allowing an attacker to have fraudulent activities accepted as valid. Fixed in version 2026.5.4.

Misskey versions from 8.63.0 up to 2026.5.4 (pre-patch) contain a vulnerability that can cause the web client to slow down or crash when it applies a malformed theme.

Misskey versions 2025.3.2 up to (but not including) 2026.5.4 have a missing permission check that allows access to certain Direct Messages data regardless of account permissions. Notes with 'specified' visibility are not affected. Fixed in version 2026.5.4.

Misskey prior to version 2026.6.0 contains a Server-Side Request Forgery (SSRF) vulnerability in the URL preview functionality. Missing network restrictions before establishing outbound connections allow a remote attacker to send HTTP requests to loopback, private, or link-local services.

Misskey prior to version 2026.6.0 contains a vulnerability in TOTP authentication where insufficient validation of used tokens allows reuse of a single-use code within its valid time step. An attacker who obtains both credentials and a TOTP code can reuse it for unauthorized actions, potentially leading to account takeover.