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Vulnerability · Published Jul 27, 2026 · Assigned by GitHub_M

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

Medium 6.3

In plain English

A medium-severity security flaw in next.js from vercel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.3Medium
Exploit odds (30 days)0.3%top 75.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
npmnext15.5.21GHSA-4633-3j49-mh5q
npmnext16.2.11GHSA-4633-3j49-mh5q

Affected products (as reported)

VendorProductVersions
vercel next.js >= 13.0.0, < 15.5.21>= 16.0.0, < 16.2.11

Weakness: CWE-116 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

References