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GHSA-4633-3j49-mh5q

Next.js: Cache confusion of response bodies for requests with bodies containing invalid UTF-8 byte sequences

Source: GitHub Advisory Database (reviewed) Moderate CVE-2026-64647

Packages

EcosystemPackageAffectedFixed in
npm next >= 13.0.0, < 15.5.21 15.5.21
npm next >= 16.0.0, < 16.2.11 16.2.11

Details

As written in the advisory (Markdown source, shown as plain text).

## Impact A server-side `fetch` with a request body may return a cached **response** body from a different request to the same URL but different body. Confidential data in the `POST`'s **response** body would then leak to unauthorized requests. Though the request itself will not be deduped. This is only an issue when receiving request bodies with a content type charset other than UTF-8. For example, the UTF-16 byte sequences for `삃삃` and `섄섄` in the request body would share the same cache. ## Workarounds If you cannot upgrade, consider only making fetch requests with UTF-8 bodies (default in Next.js). Applications using Pages Router are not vulnerable.

References

External links from the advisory. They lead to third-party sites.