CVE-2023-37015 in MME
Summary
by MITRE • 01/22/2025
Open5GS MME versions <= 2.6.4 contains an assertion that can be remotely triggered via a malformed ASN.1 packet over the S1AP interface. An attacker may send a `Path Switch Request` message missing a required `MME_UE_S1AP_ID` field to repeatedly crash the MME, resulting in denial of service.
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Analysis
by VulDB Data Team • 02/07/2025
The vulnerability identified as CVE-2023-37015 affects Open5GS MME components running versions 2.6.4 and earlier, representing a critical denial of service weakness within the 5G core network infrastructure. This issue manifests through the S1AP interface, which serves as the control plane protocol connecting eNodeB nodes to the MME in 4G/LTE networks and extends to 5G NR environments where Open5GS operates. The specific flaw resides in the assertion mechanism that validates incoming ASN.1 encoded packets, particularly those related to path switching operations within the mobility management entity. When an attacker crafts and transmits a malformed Path Switch Request message lacking the essential MME_UE_S1AP_ID field, the system fails to properly handle this validation error, leading to immediate system termination and service disruption.
The technical implementation of this vulnerability demonstrates a classic assertion failure pattern that aligns with CWE-617, which classifies assertion failures that are reachable by attackers as a direct path to system instability. The S1AP protocol operates at the control plane level of mobile networks, where it manages critical functions such as handover procedures, location updates, and session management. The Path Switch Request message specifically handles the transfer of user plane bearers between different MMEs during mobility events, making it a crucial component in maintaining uninterrupted service delivery. When the MME receives a packet with the missing MME_UE_S1AP_ID field, the assertion mechanism triggers a crash condition that cannot be recovered from gracefully, forcing the entire MME process to terminate and requiring manual intervention for restoration.
This vulnerability presents significant operational impact within 5G and 4G network environments, as the MME serves as a fundamental building block in the core network architecture responsible for managing mobility, authentication, and session control for connected users. The remote trigger capability means that adversaries can exploit this weakness from outside the network perimeter without requiring physical access or elevated privileges, making it particularly dangerous in production environments. The repeated crashing potential allows attackers to maintain persistent disruption of service, effectively rendering the affected MME unable to process legitimate user requests or manage mobility events. This type of attack directly maps to ATT&CK technique T1499.004, which covers network denial of service attacks targeting infrastructure components, and represents a clear vector for disrupting critical telecommunications services.
The remediation approach for this vulnerability requires immediate upgrade to Open5GS MME versions 2.6.5 or later, where the assertion handling has been corrected to properly validate incoming packets and gracefully handle missing fields without system termination. Network administrators should implement monitoring solutions to detect anomalous S1AP traffic patterns that might indicate exploitation attempts, while also ensuring that proper access controls and network segmentation are in place to limit exposure of the MME interface to untrusted networks. The fix addresses the underlying assertion failure by implementing proper input validation and error handling mechanisms that prevent malformed packets from causing system crashes, thereby maintaining service availability and system stability. Additionally, organizations should conduct thorough vulnerability assessments of their 5G core network deployments to identify any other instances where similar assertion-based vulnerabilities might exist within their telecommunications infrastructure components.