CVE-2025-66402: Misskey js Misskey.js's Export Data Contains Private Vulnerability

HIGH
Advisory Identifier: GHSA-496g-mmpw-j9x3
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CVSS 6.5
CWE-862
Published
Advisory Summary

CVE-2025-66402 is a HIGH (CVSS 6.5) misskey.js's export data contains private vulnerability (CWE-862: Missing Authorization) affecting Misskey js libraries in the npm ecosystem. The issue involves misskey.js's export data contains private post data. Remediation is available by upgrading affected packages to version 2025.12.0.

CVE-2025-66402 at a Glance

CVE Identifier CVE-2025-66402
GHSA Identifier GHSA-496g-mmpw-j9x3
Severity HIGH
CVSS v3.1 Base Score 6.5
CWE Classification CWE-862: Missing Authorization
Affected Product Misskey js
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2025-66402

To remediate this vulnerability, upgrade all affected Misskey js dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

misskey-js fixed: 2025.12.0 
npm install misskey-js@2025.12.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls misskey-js

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2025-66402, inspect your project dependencies using npm:

npm ls misskey-js

Analyze the terminal output to locate any version of Misskey js in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2025.12.0), your application is affected.

Note: The npm ls misskey-js command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-862: Missing Authorization, where the product does not perform an authorization check when an actor attempts to access a resource or perform an action. In Misskey js, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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.

CVE-2025-66402 Affected Misskey js Versions

1 component(s)
Fixed Versions:
2025.12.0
Product / Package Ecosystem Affected Versions Fixed Version
misskey-js
npm/misskey-js
npm
≥ 13.0.0-beta.16
< 2025.12.0
2025.12.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/misskey-dev/misskey/security/advisories/GHSA-496g-mmpw-j9x3
NVD — CVE-2025-66402 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66402
Security Fix Commit FIX COMMIT
https://github.com/misskey-dev/misskey/commit/dc77d59f8712d3fe0b73cd4af2035133839cd57b
Misskey js Source Repository REPOSITORY
https://github.com/misskey-dev/misskey

Frequently Asked Questions

What is CVE-2025-66402?
CVE-2025-66402 is a security vulnerability in Misskey js involving misskey.js's export data contains private post data under CWE-862: Missing Authorization.
Which Misskey js versions are affected?
Affected versions include releases prior to 2025.12.0 across affected packages: misskey-js.
What version fixes CVE-2025-66402?
Upgrading to 2025.12.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is misskey-js affected?
Yes, misskey-js is affected in releases prior to 2025.12.0. Upgrade your dependency to 2025.12.0 or later.
What is the CVSS score of CVE-2025-66402?
CVE-2025-66402 has a CVSS v3.1 base score of 6.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2025-66402?
CVE-2025-66402 is classified under CWE-862: Missing Authorization (The product does not perform an authorization check when an actor attempts to access a resource or perform an action.).
How can I check npm dependencies for CVE-2025-66402?
Run the dependency tree command: 'npm ls misskey-js'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-496g-mmpw-j9x3",
  "modified" : "2026-01-06T22:41:20Z",
  "published" : "2025-12-15T20:55:27Z",
  "aliases" : [ "CVE-2025-66402" ],
  "summary" : "misskey.js's export data contains private post data",
  "details" : "### Summary\n\nAfter 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.\n\n### PoC\n\n1. Create an account (X) for testing and an account (Y) for private posts on the same server.\n2. Send appropriate content from Y using \"Follow\"\n3. Send appropriate content to any user using \"Nominate\" from Y\n4. Obtain the URLs for the two posts above using Y's account.\n5. Query the URLs for the two posts using X and add them to your favorites or clips.\n6. Export your favorites or clips using X.\n7. Check the exported data.\n\nNote: Verified in v2025.11.1\n\n### Impact\n\nThis could allow an attacker to view the contents of private posts.\nIf 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "misskey-js"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "13.0.0-beta.16"
      }, {
        "fixed" : "2025.12.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/misskey-dev/misskey/security/advisories/GHSA-496g-mmpw-j9x3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-66402"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/misskey-dev/misskey/commit/dc77d59f8712d3fe0b73cd4af2035133839cd57b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/misskey-dev/misskey"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-15T20:55:27Z",
    "nvd_published_at" : "2025-12-16T00:16:02Z"
  }
}