An issue in UPF in Open5GS UPF versions up to v2.7.2 results an assertion failure vulnerability in PFCP session parameter validation. When processing a PFCP Session Establishment Request with PDN Type=0, the UPF fails to handle the invalid value propagated from SMF (or via direct attack), triggering a fatal assertion check and causing a daemon crash.
The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.
While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.