CVE-2026-64647Next.js: Response Body Cache Confusion with Invalid UTF-8 Request Bodies

Description

Next.js is a React framework for building full-stack web applications. In versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, 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. This issue has been fixed in versions 15.5.21 and 16.2.11.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• https://github.com/vercel/next.js/security/advisories/GHSA-4633-3j49-mh5q Vendor Advisory
• https://github.com/vercel/next.js/pull/96008 Issue TrackingPatch
• https://github.com/vercel/next.js/commit/025bf4a5f7b47fb7758c4ebf1c931a61c451c082 Patch
• https://github.com/vercel/next.js/releases/tag/v15.5.21 ProductRelease Notes
• https://github.com/vercel/next.js/releases/tag/v16.2.11 ProductRelease Notes