free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's BSF PUT /nbsf-management/v1/subscriptions/{subId} handler has an unsynchronized write on the global Subscriptions map. The handler first reads the map under RLock() via BSFContext.GetSubscription(subId), but if the subscription does not exist, ReplaceIndividualSubcription() writes back to the same map directly without taking the mutex (bsfContext.BsfSelf.Subscriptions[subId] = subscription). Under concurrent authenticated PUT load, one goroutine can read while another writes the map, which causes the Go runtime to abort the process with fatal error: concurrent map read and map write (Go runtime panics that come from concurrent map access bypass recover() and terminate the process). The BSF container exits with code 2 -- the entire BSF SBI surface goes down until restart. This vulnerability is fixed in 4.2.2.

Affected: Go: github.com/free5gc/bsf

### Summary free5GC's BSF `PUT /nbsf-management/v1/subscriptions/{subId}` handler has an unsynchronized write on the global `Subscriptions` map. The handler first reads the map under `RLock()` via `BSFContext.GetSubscription(subId)`, but if the subscription does not exist, `ReplaceIndividualSubcription()` writes back to the same map directly without taking the mutex (`bsfContext.BsfSelf.Subscriptions[subId] = subscription`). Under concurrent authenticated PUT load, one goroutine can read while another writes the map, which causes the Go runtime to abort the process with `fatal error: concurrent map read and map write` (Go runtime panics that come from concurrent map access bypass `recover()` and terminate the process). The BSF container exits with code `2` -- the entire BSF SBI surface goes down until restart.

This endpoint requires a valid `nbsf-management` OAuth2 access token (PR:L, NOT PR:N), so this is scored as an authenticated process-kill DoS.

### Details Validated against the BSF container in the official Docker compose lab. - Source repo tag: `v4.2.1` - Running Docker image: `free5gc/bsf:v4.2.1` - Docker validation date: 2026-03-22 - BSF endpoint: `http://10.100.200.11:8000`

Read side (locked): ```go func (c *BSFContext) GetSubscription(subId string) (*BsfSubscription, bool) { c.mutex.RLock() defer c.mutex.RUnlock()

sub, exists := c.Subscriptions[subId] return sub, exists } ```

Unsafe write side in the create-if-absent branch of `ReplaceIndividu…