CVE-2025-66402

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

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.

The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.

CVE-2025-66402 has a CVSS score of 6.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2025.12.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-66402? CVE-2025-66402 is a high-severity missing authorization vulnerability in misskey-js (npm), affecting versions >= 13.0.0-beta.16, < 2025.12.0. It is fixed in 2025.12.0. The application does not perform an authorization check before performing a sensitive operation.
2. How severe is CVE-2025-66402? CVE-2025-66402 has a CVSS score of 6.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of misskey-js are affected by CVE-2025-66402? misskey-js (npm) versions >= 13.0.0-beta.16, < 2025.12.0 is affected.
4. Is there a fix for CVE-2025-66402? Yes. CVE-2025-66402 is fixed in 2025.12.0. Upgrade to this version or later.
5. Is CVE-2025-66402 exploitable, and should I be worried? Whether CVE-2025-66402 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-66402 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-66402? Upgrade misskey-js to 2025.12.0 or later.