CVE-2025-49005 is a vulnerability identified in the Next.js framework, specifically affecting versions from 15.3.0 up to but not including 15.3.3, as well as certain versions of the Vercel CLI (41.4.1 to 42.2.0). Next.js is a popular React-based framework used for building full-stack web applications. The vulnerability is categorized under CWE-444, which pertains to inconsistent interpretation of HTTP requests, commonly known as HTTP Request/Response Smuggling. This particular flaw manifests as a cache poisoning vulnerability where, under certain conditions, page requests intended to return HTML content instead return a React Server Component (RSC) payload. This misinterpretation can cause the browser cache to store incorrect content. When deployed on Vercel's platform, the impact is limited to the browser cache, as the Vercel CDN correctly differentiates between RSC and HTML cache keys, preventing CDN-level poisoning. However, when Next.js is self-hosted and deployed with an external CDN that does not properly distinguish between these content types in cache keys, the vulnerability can lead to cache poisoning at the CDN level. This could result in users receiving malicious or unintended content from the cache, potentially leading to further exploitation such as cross-site scripting or content spoofing. The vulnerability has a CVSS v3.1 base score of 3.7, indicating a low severity level, primarily due to the complexity of exploitation (high attack complexity), no required privileges or user interaction, and limited impact (no confidentiality or availability impact, only integrity). The issue was resolved in Next.js version 15.3.3, and users are advised to upgrade to this or later versions to mitigate the risk.

For European organizations, the impact of CVE-2025-49005 depends largely on their deployment architecture. Organizations using Next.js versions 15.3.0 to 15.3.2 and deploying on Vercel's managed platform face minimal risk, as the vulnerability affects only the browser cache and does not compromise the CDN cache. However, enterprises self-hosting Next.js applications and utilizing third-party CDNs that do not properly segregate cache keys for RSC and HTML content are at risk of cache poisoning. This can lead to users receiving incorrect or malicious content, undermining the integrity of web applications. Potential consequences include erosion of user trust, brand damage, and exposure to further attacks such as cross-site scripting or phishing via manipulated cached content. Given the widespread adoption of Next.js in Europe for modern web applications, especially in sectors like e-commerce, media, and SaaS, the vulnerability could affect a broad range of services if not promptly addressed. The low CVSS score reflects limited direct impact on confidentiality and availability, but the integrity compromise in cached content can have significant reputational and operational repercussions.

European organizations should take the following specific steps to mitigate this vulnerability: 1) Upgrade all Next.js instances to version 15.3.3 or later immediately to ensure the vulnerability is patched. 2) Review CDN configurations to verify that cache keys properly distinguish between React Server Component payloads and standard HTML content. This may involve consulting CDN documentation or working with CDN providers to implement or confirm cache key segregation. 3) For self-hosted deployments, conduct thorough testing of cache behavior under various request scenarios to detect any potential cache poisoning. 4) Implement strict Content Security Policies (CSP) and Subresource Integrity (SRI) where applicable to reduce the impact of any malicious content served due to cache poisoning. 5) Monitor web application logs and user reports for anomalies that might indicate exploitation attempts. 6) Educate development and operations teams about the nature of HTTP request/response smuggling and its implications to improve detection and response capabilities. 7) Consider deploying Web Application Firewalls (WAFs) with rules tailored to detect and block HTTP request smuggling attempts.