CVE-2026-30837 is a vulnerability classified under CWE-1333, relating to inefficient regular expression complexity in the elysiajs Typescript framework, specifically in the t.String({ format: 'url' }) validator component. The vulnerability exists in versions of elysia prior to 1.4.26. The root cause is a poorly constructed regular expression used to validate URL formats, which can be manipulated by an attacker to cause catastrophic backtracking. By crafting input that repeats partial URL components such as protocol and hostname multiple times, the regex engine experiences exponential processing time, leading to a Regular Expression Denial of Service (ReDoS). This results in high CPU utilization and potential service unavailability. The vulnerability is remotely exploitable without requiring authentication or user interaction, making it a significant risk for exposed services using vulnerable elysia versions. The CVSS v3.1 base score is 7.5, indicating high severity, with the vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, meaning network attack vector, low attack complexity, no privileges or user interaction needed, unchanged scope, no confidentiality or integrity impact, but high availability impact. The vulnerability was publicly disclosed on March 10, 2026, and fixed in elysia 1.4.26. No known exploits have been reported in the wild yet, but the potential for denial-of-service attacks is significant given the nature of the flaw.

The primary impact of CVE-2026-30837 is on the availability of services using vulnerable versions of the elysiajs framework. An attacker can remotely trigger a ReDoS attack by sending specially crafted requests that exploit the inefficient regex in URL validation, causing excessive CPU consumption and potentially leading to service slowdowns or outages. This can disrupt API endpoints, degrade user experience, and cause denial of service to legitimate users. Since elysiajs is used for request validation, type inference, OpenAPI documentation, and client-server communication, the vulnerability could affect a wide range of web applications and microservices. Organizations relying on elysiajs in production environments may face operational disruptions, increased resource costs, and reputational damage if exploited. Although confidentiality and integrity are not impacted, the availability degradation can have cascading effects, especially for critical services or high-traffic applications. The ease of exploitation and lack of required authentication increase the risk profile, making it a viable vector for attackers aiming to cause service disruption.

To mitigate CVE-2026-30837, organizations should immediately upgrade elysiajs to version 1.4.26 or later, where the regex inefficiency has been addressed. In addition to patching, developers should audit their usage of the t.String({ format: 'url' }) validator and consider implementing input validation rate limiting or request throttling to reduce the impact of potential ReDoS attempts. Deploying Web Application Firewalls (WAFs) with rules to detect and block suspiciously repetitive URL patterns can provide an additional layer of defense. Monitoring application performance metrics and CPU usage can help detect anomalous spikes indicative of ReDoS attacks. For critical systems, consider isolating or sandboxing components that perform regex validation to limit resource exhaustion impact. Finally, educating developers about the risks of complex regex patterns and encouraging the use of safer validation libraries or techniques can prevent similar vulnerabilities in the future.