CVE-2025-66402: misskey.js's export data contains private post data
Summary
After adding private posts (followers, direct) that you do not have permission to view to your favorites or clips, you can export them to view the contents of the private posts.
PoC
1. Create an account (X) for testing and an account (Y) for private posts on the same server. 2. Send appropriate content from Y using "Follow" 3. Send appropriate content to any user using "Nominate" from Y 4. Obtain the URLs for the two posts above using Y's account. 5. Query the URLs for the two posts using X and add them to your favorites or clips. 6. Export your favorites or clips using X. 7. Check the exported data.
Note: Verified in v2025.11.1
Impact
This could allow an attacker to view the contents of private posts. If you have pinned private posts, this could be a real problem, as the ID of the private post can be obtained by viewing the user page on the original server.
Other sources
Misskey is an open source, federated social media platform. Starting in version 13.0.0-beta.16 and prior to version 2025.12.0, an actor who does not have permission to view favorites or clips can can export the posts and view the contents. Version 2025.12.0 fixes the issue.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2025-66402?
CVE-2025-66402 is categorized as a medium severity vulnerability allowing unauthorized access to private post content.
How do I fix CVE-2025-66402?
To mitigate CVE-2025-66402, update misskey-js to version 2025.12.0 or later.
What types of software are affected by CVE-2025-66402?
CVE-2025-66402 affects the misskey-js package versions from 13.0.0-beta.16 up to 2025.12.0.
What is the impact of CVE-2025-66402?
CVE-2025-66402 allows users to export private posts they do not have permission to view, compromising privacy.
Can I still use misskey-js with CVE-2025-66402?
Yes, you can continue using misskey-js but should upgrade to avoid the risks associated with CVE-2025-66402.