CVE-2026-64647 Next.js: Response Body Cache Confusion with Invalid UTF-8 Request Bodies
Attackers can leak confidential response data by exploiting cache confusion with invalid UTF-8 request bodies in Next.js server-side fetches.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64647?
CVE-2026-64647 is a medium-severity vulnerability in Vercel Next.js, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-116
Which versions are affected by CVE-2026-64647?
4 open source packages ship an affected version, including next. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
next npm | From 13.0.0 | 15.5.21 |
next npm | From 13.0.0 | 15.5.21 |
next npm | From 16.0.0 | 16.2.11 |
next npm | From 16.0.0 | 16.2.11 |
Products include Vercel Next.js.
How do I fix CVE-2026-64647?
Upgrade next to a fixed version for your release line: 15.5.21 or 16.2.11.
Is CVE-2026-64647 being exploited?
There is no known exploitation of CVE-2026-64647 in the wild and no public exploit code.
Other vulnerabilities in Vercel Next.js
- CVE-2025-29927 Authorization Bypass in Next.js Middleware
- CVE-2026-44578 Next.js: Server-side request forgery in applications using WebSocket upgrades
- CVE-2026-94483 Next.js: Server-Side Request Forgery in Image Optimization
- CVE-2026-64642 Next.js: Middleware / Proxy bypass in App Router applications using Turbopack and single locale
- CVE-2026-64645 Next.js: Server-Side Request Forgery in rewrites via attacker-controlled destination hostname
Sources
Also known as CLEANSTART-2026-HD84231, CLEANSTART-2026-QW21526, ECHO-8f20-024b-f6f8, GHSA-4633-3j49-mh5q, MINI-2g92-9prq-rr67, MINI-4cxc-m35w-4hxp and 3 more.