CVE-2025-7338 is a high-severity vulnerability affecting the Multer middleware for Node.js, specifically versions starting from 1.4.4-lts.1 up to but not including 2.0.2. Multer is widely used in Express.js applications to handle multipart/form-data, commonly for file uploads. The vulnerability is classified under CWE-248, which pertains to Uncaught Exception vulnerabilities. An attacker can exploit this flaw by sending a specially crafted malformed multipart upload request. This malformed request triggers an unhandled exception within the Multer middleware, causing the Node.js process to crash and resulting in a Denial of Service (DoS). The vulnerability requires no authentication or user interaction and can be exploited remotely over the network (AV:N/AC:L/PR:N/UI:N). The impact is limited to availability, as confidentiality and integrity are not affected. The vulnerability was publicly disclosed on July 17, 2025, and no known exploits are currently in the wild. The recommended remediation is to upgrade Multer to version 2.0.2 or later, where the issue has been patched. No effective workarounds exist, making timely patching critical. This vulnerability poses a significant risk to any web application relying on vulnerable Multer versions for handling file uploads, as attackers can disrupt service availability by crashing the server process handling HTTP requests.

For European organizations, this vulnerability can have considerable operational impact, especially for businesses and services that rely heavily on Node.js and Express.js frameworks with Multer middleware for file upload functionality. Industries such as e-commerce, healthcare, finance, and public sector services that provide web portals for document uploads or user-generated content are particularly at risk. A successful DoS attack could lead to service outages, loss of customer trust, potential regulatory scrutiny under GDPR due to service disruption, and financial losses from downtime. Since the vulnerability allows remote exploitation without authentication, attackers can easily target exposed endpoints. This risk is amplified for organizations with internet-facing applications that do not have additional protective layers such as Web Application Firewalls (WAFs) or rate limiting. The lack of known exploits in the wild currently provides a window for proactive mitigation, but the high CVSS score (7.5) indicates that the threat could be weaponized quickly once exploit code becomes available.

1. Immediate upgrade of Multer to version 2.0.2 or later is the most effective mitigation. This patch addresses the unhandled exception and prevents the DoS condition. 2. Implement input validation and sanitization at the application level to detect and reject malformed multipart requests before they reach Multer. 3. Deploy Web Application Firewalls (WAFs) with rules to detect and block anomalous multipart/form-data payloads that deviate from expected formats. 4. Introduce rate limiting and connection throttling on endpoints handling file uploads to reduce the risk of DoS attacks. 5. Monitor application logs and server health metrics closely for signs of crashes or abnormal request patterns indicative of exploitation attempts. 6. Consider isolating file upload handling in separate processes or containers to limit the blast radius of a crash. 7. Conduct security testing and fuzzing of multipart upload functionality to identify and remediate other potential parsing issues. 8. Maintain an incident response plan to quickly recover from potential DoS incidents, including automated restarts and failover mechanisms.