The vulnerability identified as CVE-2026-25899 affects the gofiber fiber web framework, a popular Express-inspired framework written in Go. Specifically, versions on the v3 branch prior to 3.1.0 contain a flaw in handling the fiber_flash cookie. This cookie is processed via msgpack deserialization without proper validation of the size parameter, allowing an attacker to craft a 10-character cookie value that triggers an attempt to allocate an extremely large amount of memory—up to approximately 85GB. This unbounded memory allocation is a classic example of CWE-789 (Memory Allocation with Excessive Size Value). Because the vulnerability is in the core request handling, it affects all endpoints using GoFiber v3, regardless of whether the application uses flash messages or not. The attack vector requires no authentication or user interaction, making it remotely exploitable over the network. The excessive memory allocation can cause the server process to consume all available memory, leading to denial of service (DoS) conditions. The vulnerability was publicly disclosed on February 24, 2026, with a CVSS v3.1 score of 7.5 (high severity), reflecting its ease of exploitation and impact on availability. The fix was introduced in version 3.1.0 by adding proper validation to the deserialization process to prevent excessive memory allocation.

This vulnerability poses a significant risk to organizations running web applications on GoFiber v3 prior to 3.1.0. An attacker can remotely cause a denial of service by forcing the server to allocate massive amounts of memory, potentially crashing the application or the entire host system. This can lead to service outages, degraded performance, and increased operational costs due to recovery efforts. Since no authentication is required, attackers can exploit this vulnerability at scale, potentially targeting critical web services and APIs built on GoFiber. The impact is limited to availability; confidentiality and integrity are not directly affected. However, prolonged downtime or repeated attacks could indirectly affect business continuity and reputation. Organizations relying on GoFiber for high-availability services or those exposed to the internet are particularly at risk. The absence of known exploits in the wild suggests the vulnerability is newly disclosed, but the ease of exploitation means attackers may develop exploits rapidly.

The primary mitigation is to upgrade all affected GoFiber instances to version 3.1.0 or later, where the vulnerability is fixed. If immediate upgrade is not feasible, organizations should implement strict input validation and filtering at the web server or application firewall level to block or sanitize the fiber_flash cookie. Monitoring for unusually large or malformed cookies can help detect exploitation attempts. Rate limiting and IP reputation-based blocking can reduce exposure to automated attacks. Additionally, deploying resource limits and memory usage caps at the container or operating system level can mitigate the impact of excessive memory allocation attempts. Application developers should audit their use of third-party libraries for similar deserialization vulnerabilities and apply secure coding practices to prevent unbounded allocations. Regular vulnerability scanning and patch management processes should be enforced to ensure timely updates.