CVE-2023-37034

Executive Summary

CVE-2023-37034 is a null pointer dereference vulnerability in the Mobile Management Entity (MME) component of Magma, an open-source mobile core network platform. Magma versions up to and including 1.8.0 are affected; the flaw is fixed in v1.9 via commit 08472ba98b8321f802e95f5622fa90fec2dea486. A network-adjacent attacker can crash the MME by sending a crafted S1AP Initial UE Message that omits the mandatory TAI field, resulting in a denial of service for subscribers attached to the affected MME.

The vulnerability is present in the control-plane signaling path exposed to S1-MME interactions with eNodeBs. No CVSS score was provided in the source intelligence, and there is no evidence of public exploit code or inclusion in CISA KEV. However, because the affected component is a centralized mobile-core control-plane element, successful exploitation causes significant availability impact to the LTE/EPC network segment served by the MME.

Technical Analysis

Magma is an open-source access-agnostic core network solution used to deploy LTE/5G packet core functionality in private and edge deployments. The Mobile Management Entity (MME) is the LTE control-plane node responsible for handling UE attach, authentication, tracking area updates, handover signaling, and idle-mode UE reachability. The MME communicates with radio access network equipment — eNodeBs — using the S1 Application Protocol (S1AP) over SCTP on the S1-MME interface.

The specific flaw in CVE-2023-37034 is triggered by the S1AP Initial UE Message. In normal operation, an eNodeB sends an Initial UE Message to the MME when a UE first sends a non-access-stratum (NAS) message, such as a tracking area update or attach request. The S1AP Initial UE Message is expected to carry several information elements, including the Tracking Area Identity (TAI). The TAI identifies the tracking area from which the UE is accessing the network and is required for the MME to correctly process the initial signaling message.

The vulnerability is a null pointer dereference in the MME’s S1AP message-handling logic. According to the NVD description, if an S1AP Initial UE Message is received without the expected TAI field, the MME does not appear to perform a presence check before dereferencing the TAI. This causes the MME code to access a memory address at null, resulting in a crash. The flaw is consistent with CWE-476, null pointer dereference, even though the supplied NVD record does not include an explicit CWE assignment.

From an attack-surface perspective, the vulnerable service is the S1AP listener on the MME. This is a network-adjacent attack surface: the attacker must be able to send SCTP/S1AP traffic to the MME from an eNodeB-facing network segment. In practice, this may include a compromised or rogue eNodeB, a host with access to the mobile backhaul, or any device that can inject packets into the SCTP association range used by the MME. Because S1AP is a binary ASN.1 PER-encoded protocol, the malformed message can be relatively small and does not require an established S1AP association if the MME accepts new associations from the attacker-controlled source.

The impact is limited to availability. Null pointer dereferences of this nature generally result in a crash, segmentation fault, or an unhandled exception in the affected process. They do not normally enable remote code execution or memory corruption that leads to confidentiality/integrity loss. However, the MME crash disrupts all UE registration, authentication, and mobility procedures served by that MME until the process is restarted or failed over.

The patch commit 08472ba98b8321f802e95f5622fa90fec2dea486 in Magma v1.9 addresses the issue by adding the necessary TAI presence validation before processing the Initial UE Message. The fix in v1.9 indicates that the intended behavior is to reject or drop malformed S1AP messages rather than assume mandatory IEs are always present.

At the time of this report, the EPSS score is 0.00373, placing it in the 30.5th percentile of exploited CVEs. This suggests a relatively low current likelihood of exploitation in the wild. However, because the vulnerability is simple to trigger at the protocol level and no authentication is mentioned in the NVD description, it should still be prioritized in environments where untrusted network segments can reach the MME.

Exploitation Scenarios

No public proof-of-concept or exploit code has been observed for CVE-2023-37034. The attack chain below is inferred from the vulnerability class and the S1AP protocol behavior described in the NVD record.

Step 1 — Reconnaissance and Target Identification

An attacker with network adjacency to the S1-MME interface scans for MME instances by identifying SCTP services on the standard S1AP signaling port. Magma MME deployments typically expose S1AP to one or more eNodeB gateways. An attacker who has already compromised an eNodeB or who has access to the transport network segment can identify the MME IP address through network reconnaissance or configuration leakage.

Step 2 — Triggering the Vulnerability Class

The attacker constructs an S1AP Initial UE Message packet that is structurally valid at the S1AP PDU level but intentionally omits the TAI information element. The MME begins normal processing of the message. When the internal handler attempts to read the expected TAI field from the parsed S1AP structure, the pointer is null. Because the vulnerable code path lacks a null check, dereferencing this pointer causes a crash.

This is triggered at the protocol level; no authentication bypass or session hijacking is required. The attacker only needs to be able to deliver a malformed S1AP message to the MME.

Step 3 — Payload and Execution Method

At the vulnerability-class level, the payload is a malformed control-plane protocol message, not an exploit payload targeting memory corruption for code execution. The attacker uses knowledge of the S1AP encoding rules to build an Initial UE Message with the required message type/procedure code but with the TAI IE removed. The result is an input-validation failure that leads to a null pointer dereference.

No public exploit code is available; this attack chain is inferred from the vulnerability class. It is acceptable to treat the packet as a protocol anomaly rather than a signature-based exploit.

Step 4 — Post-Exploitation Impact

After the MME process crashes, all active UE sessions attached to that MME lose control-plane connectivity. New attach requests, handovers, paging, and tracking area updates fail. Depending on the MME deployment architecture, other MMEs in a pool may not automatically absorb the affected UEs. The attacker can repeat the malformed message to prevent the MME from stabilizing, effectively causing mission-degrading denial of service.

Because the vulnerability is in a network-adjacent S1AP path rather than a subscriber-facing interface, exploitation is most relevant to attackers who already have a foothold in the RAN backhaul, an insider with eNodeB management access, or a malicious actor capable of injecting control-plane traffic into the mobile core transport network.

Impact Assessment

CVE-2023-37034 is primarily an availability vulnerability. No CVSS vector or CVSS score was published with the CVE intelligence data, so a numeric base score cannot be cited. The lack of CVSS data should not be interpreted as low severity: the affected component is the MME, which is essential to LTE control-plane operations. A crash directly impacts subscriber attach and mobility services.

The blast radius is an MME service outage within the Magma core deployment. In smaller private/edge LTE deployments, this may result in complete loss of network service for all connected UEs. In larger deployments, the MME pool may experience partial service degradation, with affected UEs unable to perform tracking area updates until either the MME restarts or the control plane re-registers.

Confidentiality and integrity impact are expected to be negligible, as a null pointer dereference does not imply memory corruption suitable for arbitrary code execution. However, repeated exploitation can be used as a persistent denial-of-service mechanism. The network-adjacent attack vector limits remote internet exposure, but it broadens risk in deployments where the RAN/backhaul is shared with lower-trust devices, such as public/private neutral-host or enterprise small-cell environments.

EPSS is 0.00373, suggesting low current exploitation likelihood. The absence from CISA KEV reinforces that there is no confirmed known-exploited status at the time of writing. Nevertheless, the vulnerability class is trivial to execute for an attacker with S1AP injection capability.

Detection Guidance

The following detection rules are templates. Not all log sources include native S1AP protocol decoding, so these rules should be adapted to the actual data plane and logging schema in use. For network-based detection, the strongest signals are malformed S1AP messages on the S1-MME interface followed by MME process termination or restart. For endpoint/host detection, MME crash logs are the primary artifact.

Sigma Rule

title: Magma MME S1AP Initial UE Message Missing TAI - CVE-2023-37034
status: experimental
description: Detects S1AP Initial UE Messages that lack the mandatory TAI field, associated with CVE-2023-37034 null pointer dereference in Magma MME.
logsource:
  category: network
  definition: S1AP traffic observed by a protocol-aware network sensor or IDS
detection:
  selection_s1ap:
    network.protocol: s1ap
    network.transport: sctp
  selection_initial_ue:
    s1ap.message_type: "Initial UE Message"
  selection_missing_tai:
    s1ap.ies.TAI: null
  condition: selection_s1ap and selection_initial_ue and selection_missing_tai
falsepositives:
  - Non-standard test traces or simulation environments that deliberately omit mandatory IEs
fields:
  - source.ip
  - destination.ip
  - destination.port
  - s1ap.procedure_code
level: high

YARA Rule

rule Magma_MME_CVE_2023_37034
{
    meta:
        author = "Threat Intelligence"
        description = "Matches Magma MME crash artifacts associated with malformed S1AP Initial UE Message missing TAI (CVE-2023-37034)."
        cve = "CVE-2023-37034"
        severity = "high"
    strings:
        $s_s1ap = "S1AP" ascii
        $s_init = "Initial UE Message" ascii
        $s_tai  = "TAI" ascii
        $s_null = "nullptr" ascii nocase
        $s_segw = "segmentation fault" ascii nocase
        $s_mme  = "MME" ascii
    condition:
        (2 of ($s_s1ap, $s_init, $s_tai, $s_mme)) and (1 of ($s_null, $s_segw))
}

Suricata IDS Rule

The following Suricata rule is an anomaly-detection template for SCTP traffic destined to the S1-MME S1AP port. The exact ASN.1 PER byte offsets will depend on the S1AP decoder used by your IDS. Validate the rule against a pcap containing legitimate S1AP traffic before production deployment.

alert sctp any any -> any 36412 (msg:"CVE-2023-37034 Magma MME S1AP Initial UE Message Missing TAI"; flow:to_server; sctp; content:"|00 08|"; depth:4; reference:cve,2023-37034; classtype:attempted-dos; sid:10037034; rev:1;)

Elastic Detection

The following Elastic EQL query correlates an SCTP connection to the S1-MME S1AP port with an MME process termination or crash. This assumes that network events and endpoint process events are both ingested into Elastic Security.

sequence by host.name
  [ network where destination.port == 36412 and network.transport == "sctp" and event.category == "network" ]
  [ process where process.name == "mme" and event.type == "end" and (exit_code != 0 or event.reason == "segfault") ]

Splunk SPL Query

The following Splunk query searches firewall/netflow, IDS, and MME host logs for SCTP traffic to the S1AP port followed by an MME crash. Adjust the sourcetypes and index names to match your environment.

(index=firewall OR index=ids) (dest_port=36412 OR network.protocol=s1ap OR app_proto=s1ap)
| stats count by src_ip, dest_ip, dest_port
| join dest_ip
    [ search index=epc_logs (sourcetype=="magma_mme" OR "mme") ("S1AP" OR "Initial UE Message" OR "segfault" OR "null pointer")
    | stats values(_time) as crash_time by host ]
| where isnotnull(crash_time)

Wazuh OSSEC Rule

<group name="magma,mme,availability,dos,">
  <rule id="100370" level="12">
    <decoded>
    <match>mme|MME|Magma</match>
    <match>S1AP</match>
    <match>Initial UE Message</match>
    <match>TAI</match>
    <regex>(segmentation fault|nullptr|null pointer|core dumped)</regex>
    <description>CVE-2023-37034 Magma MME crash likely caused by malformed S1AP Initial UE Message missing TAI</description>
    <group>cve-2023-37034, availability, denial_of_service</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence from automated tracking is currently 0/4, meaning no corroborating patch evidence has been aggregated from tracked vendor sources. However, the NVD description explicitly states that the issue is fixed in Magma v1.9 at commit 08472ba98b8321f802e95f5622fa90fec2dea486. The absence of additional vendor advisory evidence should be resolved by validating the patch commit directly against the Magma source repository and release branch.

Immediate Mitigations

• Isolate the S1-MME interface and S1AP signaling plane from untrusted network segments. Only known eNodeBs, gateways, and authorized management hosts should be able to reach the MME SCTP service.
• Configure network access control lists to restrict inbound SCTP traffic to the MME’s S1AP listener. If possible, allow only established SCTP associations from validated eNodeB source IP addresses.
• Monitor for malformed S1AP messages and repeated SCTP connection attempts to the MME from non-eNodeB sources.
• If the MME is deployed in a high-availability or pool configuration, verify that redundant MME instances can absorb traffic during a crash and failover quickly.
• Consider deploying a protocol-aware deep packet inspection device or S1AP fuzzing guard to drop S1AP messages that are missing mandatory IEs.

Patch and Upgrade Steps

• Upgrade Magma to v1.9 or later.
• If a full upgrade is not immediately possible, apply the specific fix from commit 08472ba98b8321f802e95f5622fa90fec2dea486 to the Magma MME source tree and rebuild the affected component.
• After patching, replay a crafted S1AP Initial UE Message missing the TAI field in a lab environment to confirm the MME now rejects or safely handles the malformed message instead of crashing.
• Confirm that the patched MME version passes normal attach, tracking area update, and handover regression tests.

Long-Term Hardening

• Maintain a controlled and monitored RAN backhaul environment to reduce the likelihood of a network-adjacent attacker being able to inject S1AP traffic.
• Implement S1AP message validation at the network edge if possible, dropping messages that are missing mandatory information elements.
• Ensure MME crash logs are centrally collected and monitored, with alerts for repeated termination events.
• Subscribe to Magma security advisories and update signals so that patch-confidence tracking reflects the vendor fix as soon as an advisory or release note is published.
• Follow least-privilege principles for eNodeB management interfaces and any remote access paths that cross the S1-MME network segment.

References

1. NVD – CVE-2023-37034
   https://nvd.nist.gov/vuln/detail/CVE-2023-37034

2. MITRE CVE – CVE-2023-37034
   https://cve.org/CVERecord?id=CVE-2023-37034

3. Magma source repository – fix commit 08472ba98b8321f802e95f5622fa90fec2dea486 (identified in NVD description)

4. CISA Known Exploited Vulnerabilities Catalog – CVE-2023-37034 is not currently listed
   https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No confirmed threat-actor campaigns or in-the-wild exploitation evidence were available at the time of analysis. Public PoC and exploit code for this CVE remain unknown.