CVE-2023-37021

CVE-2023-37021 affects Open5GS MME versions up to and including 2.6.4, where an assertion failure can be remotely triggered through a malformed ASN.1 packet over the S1AP interface. The issue arises when an attacker sends a UE Context Modification Failure message lacking the required MME_UE_S1AP_ID field, causing the MME to crash. This vulnerability, associated with CWE-617 (Reachable Assertion), was published on 2025-01-22 and carries a CVSS v3.1 base score of 8.6 (AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H), indicating high severity due to its network accessibility, low complexity, lack of privileges or user interaction, and scope change with high availability impact.

A remote, unauthenticated attacker can exploit this vulnerability by transmitting the malformed S1AP message to the targeted MME, leading to repeated crashes and denial of service. The attack requires no prior authentication or special access, as it leverages the S1AP interface typically exposed in 4G/5G core network deployments. Successful exploitation disrupts MME functionality, potentially halting user equipment context management and signaling for affected cells or networks.

Mitigation details are provided in the advisory at https://cellularsecurity.org/ransacked. Security practitioners should consult this reference for patch information, workarounds, or upgrade guidance for Open5GS MME.