CVE-2023-26073: Samsung Exynos Buffer Overflow Flaw

CVE-2023-26073 Overview

A heap-based buffer overflow vulnerability has been discovered in Samsung Mobile Chipset and Baseband Modem Chipset affecting multiple Exynos processors and modems. The vulnerability exists within the 5G MM (Mobility Management) message codec and occurs due to insufficient parameter validation when decoding the extended emergency number list.

This vulnerability was identified and documented by Google Project Zero researchers as part of their extensive analysis of baseband vulnerabilities in Samsung Shannon modems. The flaw allows remote attackers to potentially execute arbitrary code on the baseband processor without any user interaction, making it particularly dangerous for devices connected to cellular networks.

Critical Impact

Remote code execution on baseband processor via network-delivered malicious 5G MM messages without user interaction

Affected Products

• Samsung Exynos 850 (Mobile Chipset)
• Samsung Exynos 980 (Mobile Chipset)
• Samsung Exynos 1080 (Mobile Chipset)
• Samsung Exynos 1280 (Mobile Chipset)
• Samsung Exynos 2200 (Mobile Chipset)
• Samsung Exynos Modem 5123 (Baseband Modem)
• Samsung Exynos Modem 5300 (Baseband Modem)
• Samsung Exynos Auto T5123 (Automotive Chipset)
• Samsung Exynos W920 (Wearable Chipset)

Discovery Timeline

• March 2023 - Google Project Zero publicly disclosed baseband vulnerabilities affecting Samsung Exynos modems
• 2023-03-13 - CVE-2023-26073 published to NVD
• 2025-03-03 - Last updated in NVD database

Technical Details for CVE-2023-26073

Vulnerability Analysis

The vulnerability resides in the NrmmMsgCodec component of Samsung's Shannon baseband firmware, specifically in the code responsible for parsing extended emergency number lists within 5G NAS (Non-Access Stratum) messages. When the baseband processor receives a specially crafted 5G MM message containing an extended emergency number list, the decoding function fails to properly validate the length parameters before copying data into a heap-allocated buffer.

The Shannon baseband operates as an independent processor with its own operating system and memory space, isolated from the main application processor. However, successful exploitation of this heap overflow could allow an attacker to gain code execution within the baseband context, potentially enabling interception of cellular communications, tracking of device location, or pivoting to attack the main processor.

Google Project Zero's research demonstrated that these types of baseband vulnerabilities can be exploited remotely over the cellular network by an attacker who can send malicious packets to a target device's baseband. The attack does not require any user interaction and can be performed silently without the device owner's knowledge.

Root Cause

The root cause is classified as CWE-787 (Out-of-bounds Write). The vulnerability stems from insufficient bounds checking when processing the extended emergency number list Information Element (IE) in 5G NAS messages. The decoding function allocates a heap buffer based on expected message parameters but does not properly validate the actual data length before performing memory copy operations, leading to a heap buffer overflow condition.

Attack Vector

The attack vector is network-based, exploiting the cellular modem's protocol handling. An attacker capable of establishing a rogue base station or operating within the cellular network infrastructure could craft malicious 5G NAS messages containing oversized extended emergency number list data. When the target device's baseband modem processes this malformed message, the heap overflow occurs during the decoding phase.

The attack flow follows this pattern: The attacker sends a crafted 5G MM message to the target device through the cellular network. The Shannon baseband modem receives and begins parsing the message. When the NrmmMsgCodec component attempts to decode the extended emergency number list, insufficient length validation allows heap memory corruption, potentially leading to arbitrary code execution on the baseband processor.

Detection Methods for CVE-2023-26073

Indicators of Compromise

• Unexpected baseband crashes or modem restarts without clear cause
• Anomalous cellular network behavior or connections to unknown cell towers
• Device exhibiting unusual power consumption patterns related to modem activity
• Baseband firmware integrity check failures during device boot or security scans

Detection Strategies

• Monitor device logs for baseband crash reports or modem exception events
• Implement network-level detection for anomalous 5G NAS message patterns
• Deploy endpoint detection solutions capable of monitoring cellular modem health status
• Utilize mobile device management (MDM) solutions to track firmware versions and patch status across device fleets

Monitoring Recommendations

• Enable verbose logging on cellular network infrastructure to capture suspicious NAS message traffic
• Implement anomaly detection for devices connecting to unexpected or unauthorized cell sites
• Monitor for devices running outdated baseband firmware versions through enterprise device management
• Track security bulletin releases from Samsung for baseband-related patches

How to Mitigate CVE-2023-26073

Immediate Actions Required

• Update affected devices to the latest firmware versions that include Samsung's security patches
• Apply Samsung's March 2023 or later security maintenance release (SMR) updates
• In high-security environments, consider temporarily disabling 5G connectivity on affected devices until patches are applied
• Monitor Samsung's Product Security Updates page for official patch availability

Patch Information

Samsung has addressed this vulnerability through their security maintenance release process. Users should apply firmware updates through their device manufacturer's official update channels. For Exynos-based devices, this typically involves Samsung's monthly security patches or specific baseband firmware updates distributed through carrier and OEM update mechanisms.

Organizations deploying devices with affected Exynos chipsets should consult the Samsung Security Updates page for detailed patch information and timing.

For additional technical details about this vulnerability and related baseband security issues, refer to the Google Project Zero analysis and the associated Project Zero Issue #2396.

Workarounds

• Disable 5G connectivity and use LTE-only mode as a temporary mitigation on affected devices
• Enable airplane mode when in untrusted network environments or near potential rogue base stations
• Deploy network security controls to monitor for anomalous cellular traffic patterns
• Consider using devices with non-affected chipsets in high-security environments until patches can be verified