misskey.js's export data contains private post data

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.1 · 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 · score source

EPSS

• CVE-2025-66402: 0.31% estimated exploitation activity in the next 30 days; percentile 24.38 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

15 Dec 2025, 20:55 UTC

Last modified by the source

3 Feb 2026, 03:16 UTC

Source last checked

26 Oct 2026, 12:41 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-496g-mmpw-j9x3

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-496g-mmpw-j9x3

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# Patch Next advisory brief: CVE-2025-66402

Advisory: misskey.js's export data contains private post data
IDs: CVE-2025-66402, GHSA-496g-mmpw-j9x3
Record: https://patchnext.com/advisories/cve-2025-66402 (revision 3, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: misskey-js 2025.12.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm misskey-js: affected >= 13.0.0-beta.16, < 2025.12.0; fixed in 2025.12.0

## Suggested inspection (read-only)
- `npm ls misskey-js --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on misskey-js.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-496g-mmpw-j9x3 (OSV record GHSA-496g-mmpw-j9x3 lists affected ranges: npm misskey-js >=13.0.0-beta.16 <2025.12.0 (fixed))
- Verified: https://github.com/advisories/GHSA-496g-mmpw-j9x3 (GitHub-reviewed advisory GHSA-496g-mmpw-j9x3 lists affected ranges: npm misskey-js >=13.0.0-beta.16 <2025.12.0)

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