CVE-2025-29927 Next.js Middleware Authorization Bypass Vulnerability
Hot on the heels of the disclosure of CVE-2025-24813, a newly uncovered RCE vulnerability in Apache Tomcat—actively exploited just 30 hours after its public disclosure and PoC release—another critical security threat has now emerged. Tracked as CVE-2025-29927, the newly uncovered vulnerability has been identified in the Next.js React framework, potentially giving adversaries the green light to bypass authorization checks under specific conditions.
With the growing surge of vulnerabilities in widely used software and their rapid exploitation in real-world attacks, the demand for proactive threat detection has never been more critical. In just the first two months of 2025, NIST has identified over 10K+ vulnerabilities, many of which are already posing significant challenges for SOC teams worldwide. As cyber threats become more sophisticated, security teams must focus on early detection strategies to outpace attackers and mitigate risks before they escalate.Register to the SOC Prime Platform for collective cyber defense to access the global active threats feed serving real-time CTI and curated detection content to spot and mitigate attacks leveraging emerging CVEs on time. Explore a vast library of Sigma rules filtered by “CVE” tag and backed by a complete product suite for advanced threat detection & hunting by clicking Explore Detections below.
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CVE-2025-29927 Analysis
Recently, a critical vulnerability identified as CVE-2025-29927 was disclosed in Next.js, an open-source web framework. The flaw was assigned a high CVSS severity score of 9.1 out of 10, allowing attackers to bypass authorization checks enforced through middleware. The vulnerability affects multiple software versions from 11.x to 15.x, posing significant risks to authorization.
CVE-2025-29927 specifically impacts Next.js middleware, which is widely used for handling authorization, path rewriting, server-side redirects, and setting response headers like Content Security Policy (CSP). CVE-2025-29927 arises from a design flaw in how Next.js handles the x-middleware-subrequest header, originally meant to prevent infinite middleware loops. When middleware processes a request, runMiddleware checks for this header. If present with a specific value, the request bypasses middleware and proceeds via NextResponse.next().
The vendor warned that any host website relying solely on middleware for user authorization, without additional checks, is vulnerable to CVE-2025-29927. Attackers can exploit this by adding the header to their requests, effectively bypassing middleware-based security controls and accessing restricted resources, such as admin pages. More specifically, the vulnerability can lead to several exploits, such as enabling attackers to access protected routes without proper authorization, to bypass Content Security Policies and thus enable XSS attacks, or facilitate poison caches by bypassing middleware that sets cache controls. Given Next.js’ widespread use, the ease of exploitation—simply adding an HTTP header—makes this vulnerability particularly concerning.
While Vercel-hosted deployments are automatically secured, self-hosted applications need to apply patches or adopt CVE-2025-29927 mitigation measures. Vercel, the company behind Next.js, recommends updating to the patched software versions. The issue has been resolved in Next.js versions 14.2.25 and 15.2.3. If upgrading is not possible, a workaround is recommended for versions 11.1.4 through 13.5.6. In such cases, it’s advised to block external user requests containing the x-middleware-subrequest header from reaching the Next.js application.
Given the ease of exploitation and the significant impact of the CVE-2025-29927, it is a high-priority issue for Next.js users. Organizations are advised to adopt a proactive cybersecurity strategy to protect against potential threats, especially when they heavily rely on open-source software. SOC Prime’s complete product suite for AI-powered detection engineering, automated threat hunting, and advanced threat detection offers future-proof capabilities to enhance cyber resilience, safeguarding against increasingly sophisticated threats.
