Fiber is a popular web framework for Go, inspired by Express.js, widely used for building performant web applications. CVE-2026-25882 identifies a denial of service vulnerability caused by improper validation of array indices (CWE-129) in Fiber versions 2.x prior to 2.52.12 and 3.x prior to 3.1.0. The vulnerability stems from the framework's route registration and request matching logic, where the number of parameters in a route is not properly validated. Specifically, when a request is sent to a route with more than 30 parameters, the framework performs an unbounded write to an array used internally for matching routes. This leads to memory corruption and ultimately crashes the Fiber application, causing denial of service. The flaw requires no authentication or user interaction, making it remotely exploitable by any attacker who can send crafted HTTP requests. The issue was fixed by adding proper validation to limit the number of parameters during route registration and request processing. No known exploits have been reported in the wild, but the vulnerability poses a risk to any Fiber-based web service that accepts user-supplied route parameters without filtering. The CVSS 4.0 base score is 5.5 (medium), reflecting the ease of exploitation and impact limited to availability disruption without confidentiality or integrity compromise.

The primary impact of CVE-2026-25882 is denial of service, where an attacker can crash Fiber-based web applications by sending specially crafted requests with excessive route parameters. This can lead to service outages, degraded user experience, and potential loss of business continuity for organizations relying on Fiber for web services. Since the vulnerability does not allow code execution or data leakage, the confidentiality and integrity of data remain intact. However, the ability to remotely crash applications without authentication means attackers can disrupt critical services, potentially affecting customer-facing applications, APIs, and internal tools. Organizations with high availability requirements or those exposed to the internet are at greater risk. Additionally, repeated exploitation attempts could increase operational costs due to incident response and recovery efforts.

To mitigate this vulnerability, organizations should upgrade Fiber to version 2.52.12 or later for the v2 branch, or 3.1.0 or later for the v3 branch, where the issue is patched. If immediate upgrading is not feasible, implement input validation at the application or network level to reject requests containing more than 30 route parameters. Employ web application firewalls (WAFs) or API gateways to detect and block anomalous requests with excessive parameters. Additionally, monitor application logs for unusual request patterns that may indicate exploitation attempts. Developers should review route definitions and avoid overly complex parameterized routes that could be abused. Regularly update dependencies and conduct security testing to identify similar issues proactively. Finally, implement robust error handling to prevent application crashes from unexpected inputs.