CVE-2025-57809 is a high-severity vulnerability affecting versions of the open-source library XGrammar prior to 0.1.21. XGrammar, developed by mlc-ai, is designed for efficient, flexible, and portable structured generation. The vulnerability is classified under CWE-674, which pertains to uncontrolled recursion. Specifically, the issue arises from an infinite recursion condition in the grammar processing logic of the library. This flaw can cause the application using the vulnerable XGrammar versions to enter an infinite recursive loop, leading to stack overflow and ultimately denial of service (DoS) due to resource exhaustion. The CVSS 4.0 base score of 7.7 reflects a high severity, with the vector indicating that the vulnerability is remotely exploitable over the network without any authentication or user interaction required. The impact is primarily on availability, as the infinite recursion can crash or hang the affected application. No known exploits are currently reported in the wild, and the issue was resolved in version 0.1.21 of XGrammar. Since XGrammar is a library, the risk depends on its integration into larger software systems, which may be used in various domains requiring structured generation capabilities.

For European organizations, the impact of this vulnerability can be significant if they rely on software products or internal tools that incorporate vulnerable versions of XGrammar. The uncontrolled recursion can cause critical applications to become unresponsive or crash, leading to service outages and potential disruption of business operations. This is particularly concerning for sectors with high availability requirements such as finance, healthcare, telecommunications, and critical infrastructure. Additionally, denial of service conditions could be exploited by attackers to degrade service quality or cause operational interruptions. Since the vulnerability does not require authentication or user interaction, it could be exploited remotely, increasing the risk of automated attacks. Organizations using XGrammar in development or production environments must assess their exposure and prioritize patching to avoid potential service disruptions and maintain operational continuity.

To mitigate this vulnerability, European organizations should: 1) Identify all instances where XGrammar is used, including direct dependencies and transitive dependencies in software projects. 2) Upgrade all affected XGrammar versions to 0.1.21 or later, where the infinite recursion issue is fixed. 3) If immediate upgrading is not feasible, implement runtime safeguards such as limiting recursion depth or applying input validation to prevent malicious or malformed grammar inputs that could trigger infinite recursion. 4) Monitor application logs and performance metrics for signs of recursion-related crashes or hangs. 5) Incorporate static and dynamic analysis tools in the development pipeline to detect unsafe grammar definitions or recursive patterns. 6) Engage with software vendors or third-party providers to ensure they have patched this vulnerability in their products. 7) Establish incident response plans to quickly address potential denial of service incidents linked to this vulnerability.