CVE-2023-37016 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 a `UE Context Modification 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 • 02/07/2025
The vulnerability identified as CVE-2023-37016 affects Open5GS MME components running versions 2.6.4 and earlier, representing a critical denial of service weakness within mobile network infrastructure. This issue manifests through the S1AP protocol interface which governs communication between the MME and eNodeB in 4G LTE networks, making it particularly dangerous in production environments where network availability is paramount. The flaw resides in the assertion mechanism that validates incoming ASN.1 encoded packets, specifically targeting the UE Context Modification Response message type that is part of the standard S1AP protocol implementation.
The technical exploitation of this vulnerability occurs when an attacker crafts and transmits a malformed ASN.1 packet that lacks the required MME_UE_S1AP_ID field within a UE Context Modification Response message. This specific field is mandatory according to the S1AP specification and serves as a critical identifier for tracking user equipment contexts within the MME. When the MME processes this malformed packet, it encounters an assertion failure due to the missing field, causing the system to terminate abruptly. The assertion mechanism in the software is designed to catch programming errors or invalid states, but in this case it becomes a vector for remote exploitation rather than a protective measure.
The operational impact of this vulnerability extends beyond simple service disruption as it affects the core functionality of the mobile network infrastructure. Network operators relying on Open5GS MME implementations face potential service degradation or complete network outages when attackers exploit this weakness, particularly in environments where multiple simultaneous attacks could overwhelm the system. The vulnerability is especially concerning given that the attack requires minimal sophistication and can be executed remotely over the network, making it accessible to a broad range of threat actors. This weakness directly violates the principle of robustness in network security design, where systems should gracefully handle malformed inputs rather than crashing.
The attack vector aligns with the ATT&CK framework's T1499.004 technique for network denial of service, specifically targeting network infrastructure components. From a CWE perspective, this vulnerability maps to CWE-617: Reachable Assertion, which describes conditions where assertions can be reached through external input, and CWE-122: Heap-based Buffer Overflow, as the assertion failure may indicate underlying memory management issues. The vulnerability also reflects poor input validation practices that violate industry standards such as those outlined in NIST SP 800-53 and ISO/IEC 27001 controls for secure system design. Organizations should implement immediate mitigations including network segmentation to isolate MME components, deploying intrusion detection systems to monitor for malformed S1AP traffic patterns, and applying the vendor-provided patches to upgrade to versions beyond 2.6.4. Additionally, implementing rate limiting and connection monitoring on the S1AP interface can help detect and prevent exploitation attempts while maintaining network availability for legitimate users.