Critical Next.js Vulnerability Allows Attackers to Bypass Middleware Authorization Checks
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2025-29927 | Middleware Authorization Bypass in Vercel Next.js (CVE-2025-29927) CVE-2025-29927 is a critical (CVSS 9.1) authorization bypass in Vercel's Next.js, a widely used React framework for full-stack web applications: when an application performs its authorization checks in middleware, a remote unauthenticated attacker can bypass those checks by sending a request containing the x-middleware-subrequest header, which causes the middleware to be skipped. Successful exploitation grants access to otherwise protected routes and resources without valid credentials, with high impact on confidentiality and integrity and no availability impact (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N). All Next.js releases starting in version 1.11.4 and prior to the branch-specific fixed versions 12.3.5, 13.5.9, 14.2.25, and 15.2.3 are affected, so any Next.js application that relies on middleware for authorization is exposed. Exploitation is not yet confirmed in the provided data: the flaw is not in CISA KEV and no public proof-of-concept is catalogued, but EPSS assigns a 99.2% (100th percentile) probability of exploitation within 30 days, and national authorities such as the UK NCSC are urging immediate patching. Do: Upgrade Next.js to 12.3.5, 13.5.9, 14.2.25, or 15.2.3, matching your application's release branch. If patching is infeasible, block or strip the x-middleware-subrequest header from external requests at the reverse proxy, CDN, or WAF before they reach the Next.js application. Audit whether your applications perform authorization checks in middleware, and verify that protected routes cannot be reached without authentication after remediation. | 9.1 | 99% |
| masspotentially millions of Next.js deployments worldwide, with plausibly hundreds of thousands of sites/apps actually exposed (only those using middleware for… |
Full article280 words · extracted from thehackernews.com · click to collapse
Ravie LakshmananMar 24, 2025Vulnerability / Web Security
A critical security flaw has been disclosed in the Next.js React framework that could be potentially exploited to bypass authorization checks under certain conditions.
The vulnerability, tracked as CVE-2025-29927, carries a CVSS score of 9.1 out of 10.0.
"Next.js uses an internal header x-middleware-subrequest to prevent recursive requests from triggering infinite loops," Next.js said in an advisory.
"It was possible to skip running middleware, which could allow requests to skip critical checks—such as authorization cookie validation—before reaching routes."
It's worth noting that CVE-2025-29927 impacts only self-hosted versions that use "next start" with "output: standalone." Next.js apps hosted on Vercel and Netlify, or deployed as static exports, are not affected.
The shortcoming has been addressed in versions 12.3.5, 13.5.9, 14.2.25, and 15.2.3. If patching is not an option, it's recommended that users prevent external user requests that contain the x-middleware-subrequest header from reaching the Next.js application.
Security researcher Rachid Allam (aka zhero and cold-try), who is credited with discovering and reporting the flaw, has since published additional technical details of the flaw, making it imperative that users move quickly to apply the fixes.
"The vulnerability allows attackers to easily bypass authorization checks performed in Next.js middleware, potentially allowing attackers access to sensitive web pages reserved for admins or other high-privileged users," JFrog said.
The company also said any host website that utilizes middleware to authorize users without any additional authorization checks is vulnerable to CVE-2025-29927, potentially enabling attackers to access otherwise unauthorized resources (e.g., admin pages).
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Text extracted automatically; images, tables and formatting may be missing. Original: https://thehackernews.com/2025/03/critical-nextjs-vulnerability-allows.html