What is CVE-2025-66402?

CVE-2025-66402 is a medium-severity vulnerability in Misskey, classified under Missing Authorization. CVSS score: 6.5/10. Published 2025-12-16.

How severe is CVE-2025-66402?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Auth bypass in Misskey

CVE-2025-66402

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.

Vulnerability class: Broken Access Control

Published 2025-12-16 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.003 (21.8th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 22nd percentile — 21.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.000

Affected products

Misskey — versions 13.0.0
Misskey-Dev Misskey — versions >= 13.0.0-beta.16, < 2025.12.0

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

github.com/misskey-dev/misskey/security/advisories/GHSA-496g-mmpw-j9x3 (Exploit, Vendor Advisory)
github.com/misskey-dev/misskey/commit/dc77d59f8712d3fe0b73cd4af2035133839cd57b (Patch)

Frequently asked questions

What is CVE-2025-66402?: CVE-2025-66402 is a medium-severity vulnerability in Misskey, classified under Missing Authorization. CVSS score: 6.5/10. Published 2025-12-16.
How severe is CVE-2025-66402?: Medium severity. CVSS v3 base score is 6.5 out of 10.