CVE-2026-44573 — Next.js: Middleware / Proxy bypass in Pages Router applications using i18n

Description (CNA)

Next.js is a React framework for building full-stack web applications. From 12.2.0 to before 15.5.16 and 16.2.5, Applications using the Pages Router with i18n configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less /_next/data/<buildId>/<page>.json requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks. This vulnerability is fixed in 15.5.16 and 16.2.5.

Affected (CNA)

Vendor / product	Versions
vercel / next.js	affected >= 12.2.0, < 15.5.16; affected >= 16.0.0, < 16.2.5

CWE

CWE-863

References

https://github.com/vercel/next.js/security/advisories/GHSA-36qx-fr4f-26g5

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

redhat-SADP

A flaw was found in Next.js. Applications utilizing the Pages Router with internationalization (i18n) configured and middleware or proxy-based authorization are susceptible to unauthorized access. A remote attacker can exploit this by making locale-less /_next/data/<buildId>/<page>.json requests, which bypass the intended authorization checks. This allows the attacker to retrieve sensitive server-side rendered (SSR) JSON data from protected pages, leading to information disclosure.