CVE-2025-66367 in Exynos 850
Summary
by MITRE • 11/05/2026
Improper handling of NAS DLTransport messages may lead to a baseband crash.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability described involves an improper handling mechanism within the Non-Access Stratum (NAS) layer of cellular network protocols, specifically concerning Downlink Transport (DLTransport) messages. In mobile communication systems such as LTE and 5G NR, the NAS layer is responsible for signaling procedures between the User Equipment (UE) and the core network, including session management, mobility management, and authentication processes. The DLTransport message serves as a container for transporting higher-layer protocol data units from the network to the device. When the baseband processor receives these messages, it must parse, validate, and process them according to strict specification rules defined by 3GPP standards. A flaw in this parsing logic allows malformed or unexpected input sequences to trigger an exception condition that is not gracefully handled by the operating system or firmware of the modem chip.
This technical flaw typically manifests as a buffer overflow, integer overflow, or use-after-free error during the memory allocation and data copying phases associated with NAS message processing. Because baseband processors operate in real-time environments with limited resources and strict timing constraints, any unhandled exception often results in an immediate crash of the modem firmware. This is distinct from application-layer crashes because it affects the fundamental connectivity stack of the device. The root cause lies in insufficient input validation where the software fails to verify message length, structure integrity, or field boundaries before processing them. An attacker who can inject crafted NAS messages into the radio interface, either through a rogue base station or by manipulating signaling traffic during handover procedures, can exploit this weakness to destabilize the device's communication subsystem.
The operational impact of such a vulnerability is severe and multifaceted. The most immediate consequence is a denial-of-service condition for the affected mobile device. When the baseband crashes, the device typically reboots or enters a recovery mode, resulting in a complete loss of cellular connectivity including voice calls, SMS, and data services. In enterprise environments where devices are critical to operations, this can lead to significant downtime and productivity losses. Furthermore, if the crash state leaves memory contents unencrypted or accessible during reboot sequences, it may potentially expose sensitive information such as IMSI numbers, authentication keys, or session tokens stored in volatile memory. This aligns with CWE-20 Improper Input Validation and CWE-416 Use After Free, which are common categories for firmware-level vulnerabilities in embedded systems.
From a threat intelligence perspective, this vulnerability maps to the MITRE ATT&CK framework under techniques related to resource hijacking or denial of service against mobile devices. Specifically, it relates to T1529 System Shutdown/Reboot if an attacker can force repeated crashes to disrupt availability. It also touches upon T1498 Network Denial of Service when exploited via network-based attacks on the radio interface. The attack vector is generally considered remote but requires proximity or control over the wireless link, making it a high-risk vulnerability for devices deployed in untrusted environments such as public Wi-Fi calling scenarios or areas with compromised base stations.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. Device manufacturers should release firmware updates that enforce strict validation of NAS message structures before they are passed to the processing engine. This includes implementing bounds checking for all buffer operations, validating length fields against maximum allowed sizes defined in 3GPP specifications, and ensuring proper error handling routines that reset the state machine without crashing the entire baseband processor. Additionally, deploying intrusion detection systems at the network edge can help identify anomalous signaling patterns indicative of exploitation attempts. For end-users, keeping device software up to date is critical as vendors address these low-level firmware flaws through security patches. Security researchers and penetration testers should utilize specialized tools capable of fuzzing NAS protocols to discover similar vulnerabilities in other implementations before they are exploited in the wild.