CVE-2023-37003 in MME
Summary
by MITRE • 01/22/2025
Open5GS MME versions <= 2.6.4 contain an assertion that can be remotely triggered via a malformed ASN.1 packet over the S1AP interface. An attacker may send an `E-RAB Setup Response` 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 • 01/22/2025
The vulnerability identified as CVE-2023-37003 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 flaw manifests through the S1AP protocol interface which governs communication between the MME and eNodeB in 4G/LTE networks, though it impacts the 5G NR core network through the Open5GS implementation. The specific issue lies in the MME's handling of malformed ASN.1 packets, particularly those related to the E-RAB Setup Response message that forms part of the radio access bearer establishment process. The vulnerability stems from insufficient input validation and error handling within the MME's S1AP message processing logic, creating a condition where an assertion failure occurs when a required field is absent from the incoming message.
The technical exploitation of this vulnerability requires an attacker to send a specially crafted E-RAB Setup Response message through the S1AP interface that deliberately omits the MME_UE_S1AP_ID field, a mandatory component in the ASN.1 structure for this particular message type according to 3GPP specifications. When the MME processes this malformed packet, it encounters an assertion that fails due to the missing field, causing the process to terminate abruptly and resulting in a service disruption. This assertion failure represents a classic programming error pattern that aligns with CWE-617, which describes reachable assertions that can be triggered by external inputs. The repeated sending of such malformed packets can cause continuous service disruption, as the MME process must be restarted to restore normal operations, creating a persistent denial of service condition that affects legitimate users of the network.
The operational impact of this vulnerability extends beyond simple service interruption, as it directly affects the availability and reliability of the 5G core network infrastructure. Network operators relying on Open5GS MME implementations face potential service degradation that could impact thousands of connected devices, particularly in scenarios where the MME serves multiple eNodeBs or is part of a larger network deployment. The vulnerability's remote exploitability means that attackers do not require physical access or network proximity to cause disruption, making it particularly concerning for network security. From an adversarial perspective, this weakness aligns with ATT&CK technique T1499.004, which covers network disruption through denial of service attacks, and represents a specific implementation gap in the MME's protocol stack validation mechanisms that could be exploited to cause cascading failures in network operations.
Mitigation strategies for CVE-2023-37003 primarily involve upgrading the Open5GS MME to version 2.6.5 or later, where the assertion failure has been addressed through improved input validation and error handling. Network administrators should also implement network segmentation and access controls to limit exposure of the S1AP interface to untrusted networks, though this approach provides only partial protection. Additionally, monitoring systems should be configured to detect unusual patterns of E-RAB Setup Response messages and alert administrators to potential exploitation attempts. The fix implemented in the patched versions addresses the root cause by ensuring that the MME properly validates the presence of required fields before processing ASN.1 structures, preventing the assertion failure that previously caused the service disruption. Organizations should also consider implementing intrusion detection systems that can identify and block malformed S1AP packets, particularly those missing critical fields, as a defensive measure against similar vulnerabilities in the network infrastructure.