CVE-2025-66402

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, a social media platform, has a vulnerability in the unauthenticated fetch-rss API that lacks rate limiting and response-size restrictions and performs synchronous XML parsing. An attacker can trigger unbounded outbound HTTP requests and parsing, exhausting instance resources, amplifying requests toward third-party servers, or probing network-reachable services even when federation is disabled. This issue is fixed in version 2026.7.0.

Misskey has a vulnerability in RSS components that display feed item links from configured feeds without verifying their URL schemes. Missing URL scheme verification allows an attacker who controls feed content to provide an unsafe-scheme link that causes script execution when a user clicks it in an RSS widget. This issue is fixed in version 2026.7.0.

Misskey has a vulnerability where cleanup processing may not execute during file uploads. Repeated uploads can exhaust storage or file descriptors and deny service regardless of whether federation is enabled. This issue is fixed in version 2026.7.0.

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.