CVE-2025-53620 is a critical vulnerability affecting versions of the Qwik framework prior to 1.13.0, specifically within the @builder.io/qwik-city meta-framework. The issue arises when a Qwik Server Action QRL (Qwik Resource Locator) is executed and an invalid qfunc (Qwik function) is sent to the server. The server attempts to dynamically load the file containing the requested symbol, but if the qfunc is invalid, the server does not properly handle the thrown exception. This uncaught exception causes the Node.js process running the Qwik server to exit unexpectedly, resulting in a denial of service (DoS). The vulnerability is classified under CWE-248 (Uncaught Exception), indicating that the software fails to properly handle unexpected errors, leading to process termination. The CVSS 4.0 base score of 9.2 reflects the critical nature of this vulnerability, with a network attack vector (AV:N), low attack complexity (AC:L), no privileges or user interaction required (PR:N/UI:N), and a high impact on availability (VA:H). The vulnerability does not impact confidentiality or integrity but causes complete service disruption. No known exploits are currently reported in the wild, and the issue was fixed in version 1.13.0 of the Qwik framework. The vulnerability affects server-side Node.js environments running Qwik versions before 1.13.0, which are used to dynamically load and execute server actions based on QRLs. Attackers can remotely trigger this by sending crafted requests with invalid qfuncs, causing the server to crash and deny service to legitimate users.

For European organizations using Qwik framework versions prior to 1.13.0 in their web applications, this vulnerability poses a significant risk of denial of service. Since the flaw causes the Node.js server process to exit on receiving malformed input, attackers can remotely disrupt web services without authentication or user interaction. This can lead to service outages, impacting business continuity, customer trust, and potentially causing financial losses. Organizations relying on Qwik for critical web applications or APIs may face downtime, degraded user experience, and increased operational costs due to incident response and recovery. Additionally, repeated exploitation attempts could be used as part of larger distributed denial of service (DDoS) campaigns. The lack of confidentiality or integrity impact means data breaches are unlikely, but availability disruption alone can have severe consequences, especially for e-commerce, government, or financial services in Europe where uptime and reliability are paramount.

European organizations should immediately assess their use of the Qwik framework and identify any instances running versions prior to 1.13.0. The primary mitigation is to upgrade all affected Qwik installations to version 1.13.0 or later, where this vulnerability is fixed. In environments where immediate upgrades are not feasible, organizations should implement input validation and filtering at the network edge or application firewall to block requests containing invalid or malformed qfunc parameters. Additionally, deploying process monitoring and automatic restart mechanisms for Node.js servers can reduce downtime impact by quickly recovering from crashes. Logging and alerting on server crashes related to Qwik server actions should be enabled to detect exploitation attempts early. Organizations should also review their incident response plans to handle potential denial of service events and consider rate limiting or IP reputation-based blocking to mitigate repeated attack attempts. Finally, staying informed about any emerging exploits or patches related to this vulnerability is critical for ongoing protection.