A significant security flaw, designated as CVE-2025-49826, has been identified in Next.js, a widely-used React-based web development framework. This vulnerability enables attackers to exploit cache poisoning techniques, potentially causing Denial-of-Service (DoS) conditions by serving blank pages to users. The issue affects Next.js versions from 15.1.0 to 15.1.8, necessitating immediate attention and action from developers and organizations utilizing these versions.
Understanding the Vulnerability
The core of this vulnerability lies in a cache poisoning bug that manipulates Next.js’s response caching mechanism, particularly concerning HTTP 204 responses during static page rendering. Under specific conditions, malicious actors can poison the cache with empty responses, leading to legitimate users receiving blank pages instead of the intended content.
For this vulnerability to be exploitable, the following conditions must be met:
1. Deployment of an Affected Next.js Version: Versions between 15.1.0 and 15.1.8 are susceptible.
2. Utilization of Incremental Static Regeneration (ISR) with Cache Revalidation: This must be in production mode, either through `next start` or standalone deployment.
3. Implementation of Server-Side Rendering (SSR) with a Content Delivery Network (CDN) Configured to Cache 204 Responses: The CDN’s caching behavior plays a crucial role in the exploitation of this vulnerability.
The attack exploits a race condition within Next.js’s shared response object mechanism, where the framework improperly processes and caches HTTP 204 status codes. When successfully executed, this cache poisoning technique results in persistent DoS conditions, as the cached empty response is served to all subsequent users attempting to access the affected static pages. This impact is particularly severe for high-traffic applications that rely on ISR for performance optimization.
Risk Factors and Impact
The vulnerability’s impact is significant, with the following risk factors:
– Affected Products: Next.js versions ≥15.1.0 and <15.1.8. - Impact: Cache poisoning leading to Denial-of-Service (DoS) conditions. - Exploit Prerequisites: 1. Using an affected Next.js version (≥15.1.0 <15.1.8). 2. Routes utilizing cache revalidation with ISR in `next start` or standalone mode. 3. Routes using SSR with a CDN configured to cache 204 responses. - CVSS 3.1 Score: 7.5 (High). Remediation and Recommendations The Next.js development team has addressed this vulnerability through comprehensive code modifications targeting the root cause of the cache poisoning mechanism. The primary fix involved removing the problematic code path responsible for setting incorrect 204 responses in the static page rendering pipeline. Additionally, developers eliminated the race condition by restructuring the response caching architecture to no longer rely on shared response objects for populating the Next.js response cache. Security experts recommend immediate migration to Next.js version 15.1.8 or later, which includes the complete resolution for CVE-2025-49826. Organizations using affected versions should prioritize updating their dependencies and conducting thorough testing of their ISR and SSR implementations. Notably, applications hosted on Vercel’s platform remain unaffected due to the platform’s infrastructure design that prevents this specific attack vector. Development teams should implement comprehensive security monitoring for their Next.js applications, particularly focusing on cache behavior anomalies and unexpected 204 response patterns that could indicate ongoing exploitation attempts.
