CVE-2026-25882 is a medium-severity denial of service vulnerability identified in the Fiber web framework, a popular Express-inspired framework written in Go. The vulnerability stems from improper validation of array indices (CWE-129) during route registration and request matching. Specifically, Fiber versions prior to 2.52.12 and 3.0.1 do not enforce a limit on the number of route parameters, allowing an attacker to craft HTTP requests with more than 30 parameters. This triggers an unbounded array write operation in the route matching logic, causing the application to crash and resulting in denial of service. The vulnerability requires no authentication or user interaction and can be exploited remotely over the network. The root cause is the absence of bounds checking on the array used internally to store route parameters, which leads to memory corruption or panic conditions in Go. The issue was addressed by adding proper validation during route registration and request processing in the patched versions. No known exploits have been reported in the wild yet, but the vulnerability is straightforward to trigger given knowledge of the framework and route structure. Organizations running web applications on vulnerable Fiber versions are exposed to potential service disruption attacks.

The primary impact of CVE-2026-25882 is denial of service, which can disrupt web services relying on the Fiber framework. Attackers can remotely crash applications by sending specially crafted requests, leading to downtime, degraded user experience, and potential loss of business continuity. For organizations with critical web infrastructure built on Fiber, this could translate into significant operational and reputational damage. Since the vulnerability does not require authentication or user interaction, it can be exploited by any remote attacker, increasing the risk of widespread attacks. Additionally, denial of service conditions can be used as a smokescreen for other malicious activities or to exhaust resources. The scope includes all applications using affected Fiber versions, which may be significant given Fiber's popularity in Go web development. However, no direct data breach or code execution is indicated, limiting the impact to availability.

To mitigate this vulnerability, organizations should immediately upgrade Fiber to version 2.52.12 or later if using the v2 branch, or to version 3.0.1 or later if using the v3 branch. It is critical to audit all web applications for the Fiber framework version in use and apply patches promptly. Additionally, developers should review route definitions to ensure they do not rely on excessive numbers of parameters, ideally limiting route parameters to a safe maximum well below the vulnerable threshold. Implementing Web Application Firewalls (WAFs) or rate limiting can help detect and block abnormal requests with excessive parameters, providing a temporary protective measure. Monitoring application logs for unusual request patterns can aid in early detection of exploitation attempts. Finally, integrating automated dependency management and vulnerability scanning in the CI/CD pipeline can prevent deployment of vulnerable versions in the future.