Executive Summary

[{'type': 'paragraph', 'content': "CVE-2026-25882 is a denial of service (DoS) vulnerability in the Fiber web framework versions 2 and 3. The issue occurs because Fiber does not validate the number of parameters in a route during registration. Fiber uses a fixed-size array of 30 elements to store route parameters, but if a route with more than 30 parameters is registered, the framework attempts to write beyond this array's bounds during request matching."}, {'type': 'paragraph', 'content': 'When an attacker sends a request to such a route with more than 30 parameters, the server crashes with a runtime panic due to an out-of-range array index. This crash causes a denial of service by disrupting the application.'}, {'type': 'paragraph', 'content': 'The vulnerability is fixed in Fiber version 2.52.12 and 3.1.0.'}] [1]

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Impact Analysis

This vulnerability can cause a complete service disruption by crashing the Fiber-based application when it processes a specially crafted HTTP request targeting a route with more than 30 parameters.

The impact includes denial of service due to server crashes, which can lead to cascading failures in microservices architectures, interfere with auto-scaling mechanisms, and generate excessive log entries (log flooding).

Exploitation requires no authentication and can be triggered remotely with a single HTTP request, making it relatively easy for attackers to cause disruption.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring application logs for panic patterns indicating exploitation attempts, specifically runtime panics caused by out-of-range array index errors related to route parameters exceeding 30.'}, {'type': 'paragraph', 'content': 'You can audit your Fiber application routes to identify any routes registered with more than 30 parameters, as these are vulnerable to triggering the denial of service.'}, {'type': 'paragraph', 'content': 'To detect exploitation attempts on your network, you can look for HTTP requests with paths containing more than 30 segments (parameters), which are unusual and may indicate an attack.'}, {'type': 'paragraph', 'content': 'Suggested commands include searching application logs for panic messages similar to: "runtime error: index out of range [30] with length 30".'}, {'type': 'list_item', 'content': "Example command to search logs for panic errors (Linux): grep -i 'runtime error: index out of range' /path/to/your/app/logs/*"}, {'type': 'list_item', 'content': 'Example command to detect suspicious HTTP requests with more than 30 path segments in access logs: awk -F" " \'{split($7,a,"/"); if(length(a) > 31) print $0}\' /path/to/access.log'}, {'type': 'list_item', 'content': 'Audit your route definitions in the source code to check for routes with more than 30 parameters.'}] [1]

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Mitigation Strategies

Immediate mitigation steps include upgrading the Fiber framework to a patched version: v2.52.12 for the v2 branch or v3.1.0 for the v3 branch, where the vulnerability is fixed.

If upgrading is not immediately possible, audit all routes to ensure none have more than 30 parameters, and disable or validate dynamic route registration to prevent routes with excessive parameters.

Implement aggressive rate limiting on your application to reduce the impact of potential denial of service attacks exploiting this vulnerability.

Monitor application logs for panic patterns that indicate exploitation attempts and respond accordingly.

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