GitHub Security Advisory: GHSA-98cp-84m9-q3qp
Package: github.com/free5gc/pcf (GO)
Severity: HIGH (CVSS 7.5)
CWE: CWE-400: Uncontrolled Resource Consumption
Vulnerable versions: < 1.4.3
Patched in: 1.4.3

Summary: free5GC PCF: Memory Leak via CORS Middleware Registration in HTTP Handler Leads to Denial of Service

Details:
## Summary

A memory leak vulnerability in the free5GC PCF (Policy Control Function) allows any unauthenticated attacker with network access to the PCF SBI interface to cause uncontrolled memory growth by sending repeated HTTP requests to the OAM endpoint. The root cause is a `router.Use()` call inside an HTTP handler that registers a new CORS middleware on every incoming request, permanently growing the Gin router's handler chain. This leads to progressive memory exhaustion and eventual Denial of Service of the PCF, preventing all UEs from obtaining AM and SM policies and blocking 5G session establishment.

## Details

**File:** `free5gc/pcf/internal/sbi/api_oam.go`  
**Function:** `setCorsHeader()`, called by `HTTPOAMGetAmPolicy()`

The function `setCorsHeader()` invokes `s.router.Use()` on every incoming HTTP request:

```go
func (s *Server) setCorsHeader(c *gin.Context) {
    // BUG: router.Use() inside a handler — executes on every request
    s.router.Use(cors.New(cors.Config{
        AllowMethods:     []string{"GET", "POST", "OPTIONS", "PUT", "PATCH", "DELETE"},
        AllowAllOrigins:  true,
        AllowCredentials: true,
        MaxAge:           CorsConfigMaxAge,
    }))
    // Redundant manual header setting
    c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
    c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
    // ...
}

func (s *Server) HTTPOAMGetAmPolicy(c *gin.Context) {
    s.setCorsHeader(c) // ← called on every GET /npcf-oam/v1/am-policy/:supi
    // ...
}
```
In the Gin framework, `router.Use()` appends a new `HandlerFunc` to the router's internal middleware slice. This operation is **not idempotent** — it does not replace existing middleware but appends a new instance on every call. After N requests, Gin executes N CORS middleware instances before reaching the actual handler:

Request N → [cors_mw_1 → cors_mw_2 → ... → cors_mw_N → actual_handler]

Since `s.router` holds a permanent reference to the accumulated middleware slice, the Go garbage collector cannot free this memory. The additional issue of `AllowAllOrigins: true` combined with `AllowCredentials: true` also constitutes a CORS misconfiguration (forbidden by the CORS specification), though this is secondary to the memory leak.

**Fix:** Move `router.Use(cors.New(...))` to the server initialization function (called once at startup), and remove `setCorsHeader()` from all handlers entirely:

```go
// ✅ server.go — called once at startup
func (s *Server) initRouter() {
    s.router.Use(cors.New(cors.Config{
        AllowMethods:     []string{"GET", "POST", "OPTIONS", "PUT", "PATCH", "DELETE"},
        AllowOrigins:     []string{"https://trusted-origin.example.com"},
        AllowCredentials: false,
        MaxAge:           CorsConfigMaxAge,
    }))
}
```
## PoC

**Environment:**
- free5GC v4.2.1 (commit `df535f55`, build `2026-03-04`)
- PCF container IP: `10.22.22.6`, port `80`
- Attacker: any container on the same Docker network (tested fr