CVE-2026-25882 Overview
CVE-2026-25882 is a denial of service vulnerability affecting Fiber, a popular Express-inspired web framework written in Go. This vulnerability allows remote attackers to crash applications by sending requests to routes configured with more than 30 parameters. The flaw stems from missing validation during route registration combined with an unbounded array write during request matching, classified under CWE-129 (Improper Validation of Array Index).
Critical Impact
Remote attackers can cause application crashes and service disruption by exploiting routes with excessive parameters, leading to availability impacts for production Fiber-based services.
Affected Products
- Fiber v2 (versions prior to 2.52.12)
- Fiber v3 (versions prior to 3.1.0)
- Go applications using vulnerable Fiber framework versions
Discovery Timeline
- 2026-02-24 - CVE-2026-25882 published to NVD
- 2026-02-24 - Last updated in NVD database
Technical Details for CVE-2026-25882
Vulnerability Analysis
This denial of service vulnerability exists within Fiber's route handling mechanism. The framework fails to properly validate the number of parameters during route registration, allowing routes with more than 30 parameters to be defined. During request matching, an unbounded array write operation occurs when processing these excessive parameters, resulting in application crashes.
The vulnerability is exploitable over the network without requiring authentication or user interaction. While the confidentiality and integrity impacts are none, the availability impact allows attackers to disrupt service operations by targeting vulnerable route configurations.
Root Cause
The root cause is improper validation of array index (CWE-129) in Fiber's path handling logic. The framework does not enforce a boundary check on the number of route parameters during registration. When a request matches a route with more than 30 parameters, the internal array used to store parameter values is written beyond its allocated bounds.
The vulnerable code exists in the path.go file of both the main (v3) and v2 branches of the Fiber framework. The v3 path.go implementation and v2 path.go implementation both contain this validation gap.
Attack Vector
The attack vector is network-based and requires no special privileges or user interaction. An attacker can exploit this vulnerability by:
- Identifying a Fiber application with routes containing more than 30 parameters
- Sending crafted HTTP requests to these vulnerable routes
- Triggering the unbounded array write during request matching
- Causing the application to crash, resulting in denial of service
The vulnerability can be repeatedly exploited to maintain service disruption until the affected route configuration is modified or the application is patched.
Detection Methods for CVE-2026-25882
Indicators of Compromise
- Unexpected application crashes or restarts in Fiber-based services
- Error logs indicating array index out of bounds or panic conditions in path.go
- Increased incoming requests targeting routes with numerous path parameters
- Service availability degradation patterns consistent with DoS attacks
Detection Strategies
- Monitor application logs for Go panic messages originating from route matching functions
- Implement request logging to identify unusual patterns in path parameter usage
- Use application performance monitoring to detect sudden crash events
- Review route configurations to identify routes with more than 30 parameters
Monitoring Recommendations
- Configure alerting for application crash events in production Fiber services
- Implement rate limiting on routes with multiple path parameters
- Deploy health check endpoints to detect service availability issues
- Enable verbose logging during incident response to capture exploitation attempts
How to Mitigate CVE-2026-25882
Immediate Actions Required
- Upgrade Fiber v2 applications to version 2.52.12 or later
- Upgrade Fiber v3 applications to version 3.1.0 or later
- Review existing route configurations and reduce parameter count where feasible
- Implement request filtering at the load balancer or WAF level for routes with excessive parameters
Patch Information
The Fiber maintainers have released patches addressing this vulnerability in both major version branches. The fix was implemented via Pull Request #3962, which adds proper validation to enforce parameter count limits during route registration. For complete details, refer to the GitHub Security Advisory GHSA-mrq8-rjmw-wpq3.
| Version Branch | Patched Version |
|---|---|
| v2 | 2.52.12 |
| v3 | 3.1.0 |
Workarounds
- Audit and refactor routes to use fewer than 30 parameters
- Implement application-level middleware to validate and limit incoming parameter counts
- Deploy a reverse proxy or WAF with rules to block requests with excessive path segments
- Consider using query parameters or request body fields as alternatives to numerous path parameters
# Update Fiber v2 to patched version
go get github.com/gofiber/fiber/v2@v2.52.12
# Update Fiber v3 to patched version
go get github.com/gofiber/fiber/v3@v3.1.0
# Verify installed version
go list -m github.com/gofiber/fiber/v2
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
