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CVE-2026-64645 – SSRF / Open Redirect – Next.js 12.0.0–15.5.20 and 16.0.0–16.2.10

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Summary

CVE-2026-64645 is a Server-Side Request Forgery (SSRF) and Open Redirect vulnerability in Next.js, the widely deployed React full-stack web framework maintained by Vercel. It affects versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, and carries a CVSS 4.0 score of 8.3 (High). When a rewrites() or redirects() configuration rule dynamically constructs an external destination hostname from attacker-controlled request input, the intended hostname suffix can be bypassed — enabling the Next.js server to be forced to proxy requests to any arbitrary host.

Technical details

  • Root cause: Next.js interpolates user-controlled dynamic path segments (e.g., regex capture groups) directly into the destination URL of rewrites() and redirects() rules without validating the resulting hostname. This allows attacker-supplied values containing dots to escape the intended hostname suffix.
  • Exploit mechanism: The attack leverages DNS treatment of a trailing dot as a fully-qualified domain name (FQDN). For example, a rule such as destination: 'https://:tenant.api.example.com' can be exploited by supplying the tenant value attacker.com. — DNS resolves attacker.com. (the FQDN root) rather than the intended attacker.com..api.example.com, causing the Next.js server to contact the attacker-controlled host instead.
  • Attack vector: Network-accessible, no authentication required, no user interaction needed.
  • Prerequisites: The application must use rewrites() or redirects() rules that build destination hostnames from request-controlled input (e.g., URL path parameters or query parameters); this is not a default Next.js configuration.
  • Impact (rewrites): Next.js proxies the request to the arbitrary host and serves the response from the application’s origin — enabling full Server-Side Request Forgery. Attackers can probe internal network services, reach cloud metadata endpoints (e.g., AWS Instance Metadata Service at 169.254.169.254), and exfiltrate sensitive data.
  • Impact (redirects): The user’s browser is redirected to an attacker-controlled domain — enabling Open Redirect attacks.

Affected software

  • Next.js 12.0.0 through 15.5.20 (inclusive)
  • Next.js 16.0.0 through 16.2.10 (inclusive)

Severity

CVSS 4.0 Base Score: 8.3 (High)
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:L/SI:L/SA:N

Mitigation and recommended actions

  • Immediate — apply vendor patches:
    • Upgrade to Next.js 15.5.21 (Maintenance LTS): npm install [email protected]
    • Upgrade to Next.js 16.2.11 (Active LTS): npm install [email protected]
    • Fixes are also included in Next.js 16.3 canary (v16.3.0-canary.92) and preview (v16.3.0-preview.7) releases.
  • If immediate patching is not feasible — harden rewrite/redirect configurations:
    • Restrict dynamic destination segments to hostname-safe characters only (alphanumeric and hyphens) using strict regex constraints, e.g.: value: '(?<tenant>[a-z0-9-]+)'. This prevents dot characters from being injected into the destination hostname.
    • Audit all rewrites() and redirects() rules in next.config.js for dynamic segments sourced from request input.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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