The vulnerability identified as CVE-2026-23956 affects the seroval library, a JavaScript utility designed to facilitate value stringification, including complex structures beyond the capabilities of the standard JSON.stringify method. In versions 1.4.0 and below, the library allows overriding RegExp serialization. An attacker can exploit this by providing extremely large regular expression patterns or patterns that cause catastrophic backtracking during deserialization. This leads to excessive consumption of JavaScript runtime memory, potentially exhausting available resources and causing the application to become unresponsive or crash. The root cause is inefficient handling of regular expressions (CWE-1333), which results in a denial of service condition (ReDoS). The vulnerability is remotely exploitable without any privileges or user interaction, making it a significant risk in exposed environments. The issue has been addressed in seroval version 1.4.1 by improving the handling of RegExp serialization to prevent memory exhaustion and catastrophic backtracking. Although no known exploits are currently reported in the wild, the high CVSS score of 7.5 reflects the potential impact on availability and ease of exploitation.

For European organizations, the primary impact of this vulnerability is on the availability of services that rely on the seroval library for JavaScript value serialization and deserialization. Applications using vulnerable versions may experience crashes or severe performance degradation when processing maliciously crafted regular expressions, leading to denial of service. This can disrupt web services, APIs, or backend processes, potentially affecting customer-facing applications or internal tools. Since the vulnerability does not compromise confidentiality or integrity, data breaches are unlikely; however, service outages can result in operational downtime, loss of productivity, and reputational damage. Organizations in sectors with high reliance on JavaScript-based services, such as finance, e-commerce, and public services, may face heightened risks. Additionally, the vulnerability’s remote exploitability without authentication increases the threat landscape, especially for internet-facing applications.

European organizations should immediately upgrade all instances of the seroval library to version 1.4.1 or later, where the vulnerability is fixed. For environments where immediate upgrading is not feasible, implement input validation and sanitization to restrict or reject overly large or complex regular expression patterns before they reach the seroval deserialization process. Employ runtime monitoring to detect abnormal memory usage or performance degradation indicative of ReDoS attacks. Consider deploying Web Application Firewalls (WAFs) with rules to identify and block malicious regular expression payloads targeting this vulnerability. Additionally, conduct code audits to identify any custom overrides of RegExp serialization that may be vulnerable. Incorporate this vulnerability into incident response plans and ensure that development teams are aware of the risks associated with inefficient regular expression handling. Finally, maintain up-to-date dependency management and vulnerability scanning to promptly identify and remediate similar issues in third-party libraries.