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

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-27 · updated 2026-10-24
Weakness: CWE-116

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.

Affected products

Next.js: from 13.0.0 before 15.5.21; from 16.0.0 before 16.2.11 — fixed in 15.5.21, 16.2.11
Npm Next: from 13.0.0 before 15.5.21; from 16.0.0 before 16.2.11 — fixed in 15.5.21, 16.2.11

How to fix

Upgrade to a fixed version: Next.js 15.5.21, 16.2.11; Npm Next 15.5.21, 16.2.11. Check the vendor advisory for mitigations.

References

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