How severe is CVE-2025-66402?

No CVSS score has been assigned to CVE-2025-66402 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-66402?

CVE-2025-66402 affects the following packages: misskey-js (npm). Ecosystems affected: npm.

How do I fix CVE-2025-66402?

Update misskey-js to 2025.12.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66402 is resolved across your whole dependency graph.

How do I detect CVE-2025-66402 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for misskey-js, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2025-66402 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2025-66402 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-66402 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-66402?

CVE-2025-66402 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 23th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-66402?

CVE-2025-66402 is classified as CWE-862 (CWE-862). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-66402 published, and has it been updated?

CVE-2025-66402 was published on December 15, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2025-66402 — misskey-js

Fix: misskey-dev/misskey@dc77d59

CVE-2025-66402 is a CWE-862 vulnerability in misskey-js. A fix is available for misskey-js — see the affected versions and patch details below.

misskey.js's export data contains private post data

Also known asGHSA-496g-mmpw-j9x3

Published

Dec 15, 2025

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 24, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66402.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs23th percentile — riskier than 23% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

1other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

misskey-jsnpm

1Kdownloads / week

Description

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

Create an account (X) for testing and an account (Y) for private posts on the same server.
Send appropriate content from Y using "Follow"
Send appropriate content to any user using "Nominate" from Y
Obtain the URLs for the two posts above using Y's account.
Query the URLs for the two posts using X and add them to your favorites or clips.
Export your favorites or clips using X.
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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`misskey-js`	≥ 13.0.0-beta.16&&< 2025.12.0	2025.12.0`npm install misskey-js@2025.12.0`

Affected Products

1 product · 37 configurations

Application

misskeymisskey

≥ 13.1.0 && < 2025.12.0

1 version

13.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for misskey-js, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update misskey-js to 2025.12.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66402 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### 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

O3 Security · Impact-Aware SCA

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