Description

Fiber has a Denial of Service Vulnerability via Route Parameter Overflow A denial of service vulnerability exists in Fiber v2 and v3 that allows remote attackers to crash the application by sending requests to routes with more than 30 parameters. The vulnerability results from missing validation during route registration combined with an unbounded array write during request matching.

Affected Versions

Fiber v3.0.0-rc.3 and earlier v3 releases

Fiber v2.52.10 and potentially all v2 releases (confirmed exploitable)

Both versions share the same vulnerable routing implementation

Vulnerability Details

Root Cause

Both Fiber v2 and v3 define a fixed-size parameter array in ctx.go:

const maxParams = 30

type DefaultCtx struct {
    values [maxParams]string  // Fixed 30-element array
    // ...
}

The router.go register() function accepts routes without validating parameter count. When a request matches a route exceeding 30 parameters, the code in path.go performs an unbounded write:

v3: path.go:514

v2: path.go:516

// path.go:514 - NO BOUNDS CHECKING
params[paramsIterator] = path[:i]

When paramsIterator >= 30, this triggers:

panic: runtime error: index out of range [30] with length 30

Attack Scenario

Application registers route with >30 parameters (e.g., via code or dynamic routing):

app.Get("/api/:p1/:p2/:p3/.../p35", handler)

Attacker sends matching HTTP request:

curl http://target/api/v1/v2/v3/.../v35

Server crashes during request processing with runtime panic

Proof of Concept

For Fiber v3

package main

import (
	"fmt"
	"net/http"
	"time"
	"github.com/gofiber/fiber/v3"
)...
Show more

Output:

Registering route: /test/:p1/:p2/:p3/:p4/:p5/:p6/:p7/:p8/:p9/:p10...
✓ Registration succeeded (NO PANIC)

🔴 Sending exploit request...
Expected: panic at path.go:514 params[paramsIterator] = path[:i]

panic: runtime error: index out of range [30] with length 30
...
Show more

For Fiber v2

package main

import (
	"fmt"
	"net/http"
	"time"
	"github.com/gofiber/fiber/v2"
)...
Show more

Output (v2):

Registering route: /test/:p1/:p2/:p3/:p4/:p5/:p6/:p7/:p8/:p9/:p10...
✓ Registration succeeded (NO PANIC)

🔴 Sending exploit request...
Expected: panic at path.go:516 params[paramsIterator] = path[:i]

panic: runtime error: index out of range [30] with length 30
...
Show more

Impact

Exploitation Requirements

No authentication required

Single HTTP request triggers crash

Trivially scriptable for sustained DoS

Works against any route with >30 parameters

Real-World Impact

Public APIs: Remote DoS attacks on vulnerable endpoints

Microservices: Cascade failures if vulnerable service is critical

Auto-scaling: Repeated crashes prevent proper recovery

Monitoring: Log flooding and alert fatigue

Likelihood

HIGH - Exploitation requires only:

Knowledge of route structure (often public in APIs)

Standard HTTP client (curl, browser, etc.)

Single malformed request

Workarounds

Until patched, users should:

Audit Routes: Ensure all routes have ≤30 parameters

# Search for potential issues
grep -r "/:.*/:.*/:.*" . | grep -v node_modules

Disable Dynamic Routing: If programmatically registering routes, validate parameter count:

paramCount := strings.Count(route, ":")
if paramCount > 30 {
    log.Fatal("Route exceeds maxParams")
}

Rate Limiting: Deploy aggressive rate limiting to mitigate DoS impact

Monitoring: Alert on panic patterns in application logs

Timeline

2024-12-24: Vulnerability discovered in v3 during PR #3962 review

2024-12-25: Proof of concept confirmed exploitability in v3

2024-12-25: Vulnerability confirmed to also exist in v2 (same root cause)

2024-12-25: Security advisory created

References

v3 Related PR: https://github.com/gofiber/fiber/pull/3962 (UpdateParam feature with defensive checks, doesn't fix root cause)

Vulnerable Code Locations:

v3: path.go:514

v2: path.go:516

Credit

Discovered by: @sixcolors (Fiber maintainer) and @TheAspectDev

Mitigation

Aliases

References