CVE-2025-50537 is a stack overflow vulnerability identified in eslint, a widely used JavaScript linting tool, specifically in versions before 9.26.0. The vulnerability arises during the serialization process of test cases containing circular references within the RuleTester.run() method. This method validates test cases and checks for duplicates by invoking an internal function, checkDuplicateTestCase(), which relies on isSerializable() to determine if test case objects can be serialized. When an object with circular references is passed, isSerializable() enters infinite recursion because it does not handle circular references properly, leading to a stack overflow condition. This can cause the eslint process to crash, resulting in denial of service during linting or testing phases. The vulnerability does not appear to allow remote code execution or privilege escalation, and exploitation requires the attacker to supply specially crafted test cases, typically in a development or CI/CD environment. No public exploits have been reported to date. The issue was reserved in June 2025 and published in January 2026, with no CVSS score assigned yet. The fix involves updating eslint to version 9.26.0 or later, where serialization logic has been improved to handle circular references safely. This vulnerability primarily impacts development workflows that use eslint's RuleTester for validating linting rules, potentially disrupting automated testing and continuous integration pipelines.

For European organizations, the primary impact of CVE-2025-50537 is disruption of software development and testing processes. Since eslint is a popular tool in JavaScript development, organizations relying on it for code quality assurance may experience crashes or failures in their linting and testing pipelines if vulnerable versions are used with test cases containing circular references. This can delay development cycles, reduce developer productivity, and increase the risk of shipping code without proper linting validation. Although the vulnerability does not directly compromise confidentiality or integrity, denial of service in build environments can have downstream effects on release schedules and operational stability. Organizations with automated CI/CD pipelines that incorporate eslint RuleTester are particularly at risk. The absence of known exploits reduces immediate threat but does not eliminate the risk of targeted attacks or accidental disruptions. European companies in sectors with heavy software development, such as finance, telecommunications, and technology, may face operational impacts if mitigation is not applied promptly.

To mitigate CVE-2025-50537, European organizations should: 1) Upgrade eslint to version 9.26.0 or later, where the serialization issue has been addressed. 2) Audit existing test cases used with RuleTester to identify and refactor or remove any that include circular references, preventing infinite recursion during serialization. 3) Integrate static analysis or linting checks in CI/CD pipelines to detect usage of vulnerable eslint versions and prevent deployment of problematic test cases. 4) Educate development teams about the risks of circular references in test objects and encourage best practices in test case design. 5) Monitor eslint release notes and security advisories for any further updates or related vulnerabilities. 6) If upgrading immediately is not feasible, consider isolating eslint runs in containerized or sandboxed environments to limit the impact of potential crashes. 7) Implement robust error handling in build scripts to gracefully manage eslint failures and avoid cascading pipeline disruptions.