CVE-2025-26781: Samsung Exynos W920 Firmware DoS Flaw

CVE-2025-26781 Overview

CVE-2025-26781 is a Denial of Service vulnerability affecting the L2 layer in multiple Samsung Exynos mobile processors, wearable processors, and modems. The vulnerability stems from incorrect handling of RLC AM (Radio Link Control Acknowledged Mode) Protocol Data Units (PDUs), which can be exploited remotely to cause a denial of service condition on affected devices.

Critical Impact

Network-based attackers can remotely disrupt cellular connectivity and device availability on Samsung Exynos-powered mobile devices and wearables without requiring authentication or user interaction.

Affected Products

• Samsung Exynos Mobile Processors: 980, 990, 850, 1080, 2100, 1280, 2200, 1330, 1380, 1480
• Samsung Exynos Wearable Processors: 9110, W920, W930
• Samsung Modems: 5123, 5300, 5400

Discovery Timeline

• October 20, 2025 - CVE-2025-26781 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2025-26781

Vulnerability Analysis

This vulnerability exists in the Layer 2 (L2) data link layer implementation of Samsung's Exynos chipset family. The L2 layer is responsible for handling the Radio Link Control (RLC) protocol, which manages data transmission reliability over the cellular radio interface. Specifically, the issue resides in the RLC Acknowledged Mode (AM) PDU processing logic.

RLC AM is a critical protocol mode used in LTE and 5G networks that provides reliable data delivery through retransmission mechanisms. The vulnerability manifests when the affected processors receive malformed or specially crafted RLC AM PDUs, leading to improper input validation (CWE-20). When exploited, this causes the modem or processor to enter an unrecoverable state, resulting in denial of service.

The attack can be executed remotely over the network without requiring any privileges or user interaction, making it particularly dangerous for mobile devices relying on these processors for cellular connectivity. The impact is limited to availability; there is no compromise of confidentiality or integrity.

Root Cause

The root cause is improper input validation (CWE-20) in the RLC AM PDU handling code within the L2 layer firmware. The affected code fails to properly validate boundaries or parameters within incoming RLC AM PDUs before processing them. When encountering malformed PDU structures or unexpected field values, the parsing logic does not gracefully handle the error condition, leading to processor instability or crash.

Attack Vector

The attack vector is network-based, targeting the cellular modem interface of affected Samsung devices. An attacker positioned within radio range or with the ability to inject traffic into the cellular network path could send specially crafted RLC AM PDUs to trigger the vulnerability.

The attack requires no authentication or user interaction, and can potentially be executed against any device with an affected Exynos processor that is connected to a cellular network. The scope remains unchanged, meaning the impact is contained to the vulnerable component itself.

The vulnerability mechanism involves crafting malformed RLC AM Protocol Data Units that exploit the improper validation in the L2 layer. When processed by the vulnerable firmware, these malformed PDUs cause the modem to fail, disrupting cellular connectivity. See the Samsung CVE-2025-26781 Advisory for additional technical details.

Detection Methods for CVE-2025-26781

Indicators of Compromise

• Unexpected cellular modem crashes or restarts on Exynos-powered devices
• Repeated loss of cellular connectivity without environmental explanation
• Baseband processor exception logs or crash dumps in device diagnostics
• Anomalous RLC layer error rates in cellular network monitoring

Detection Strategies

• Monitor device health telemetry for abnormal modem restart patterns on managed Samsung devices
• Implement MDM (Mobile Device Management) solutions to track and alert on cellular connectivity anomalies across the fleet
• Review baseband firmware crash logs for L2/RLC-related exceptions on affected device models
• Deploy network-level monitoring to detect unusual RLC AM PDU patterns if accessible

Monitoring Recommendations

• Enable verbose logging on MDM platforms for Samsung devices running affected Exynos processors
• Configure alerts for devices experiencing multiple cellular connectivity drops within short timeframes
• Track firmware versions across the device fleet to identify unpatched Exynos devices
• Coordinate with network operations teams to monitor for anomalous signaling traffic patterns

How to Mitigate CVE-2025-26781

Immediate Actions Required

• Identify all devices in your environment running affected Samsung Exynos processors or modems
• Prioritize firmware updates for devices handling sensitive communications or critical operations
• Monitor the Samsung Security Updates page for patch availability
• Consider temporary network isolation for highly sensitive devices until patches are applied

Patch Information

Samsung has published security advisories addressing this vulnerability. Organizations should apply firmware updates as they become available from Samsung through the official Samsung Security Updates portal. For specific patch details related to this CVE, refer to the Samsung CVE-2025-26781 Advisory.

Device manufacturers using these Exynos chipsets should coordinate with Samsung to obtain and distribute patched firmware to end users. End users should ensure their devices are set to receive automatic updates and apply any pending security patches promptly.

Workarounds

• No direct workarounds are available for this vulnerability due to its low-level firmware nature
• Implement network segmentation where possible to limit exposure of critical devices
• Use Wi-Fi connectivity as the primary connection method when cellular is not essential
• Consider deploying endpoint protection solutions that can detect anomalous modem behavior

# Check Samsung device firmware version via ADB
adb shell getprop ro.build.version.baseband

# Verify Exynos processor model
adb shell getprop ro.hardware

# Monitor for modem crashes in device logs
adb logcat -b radio | grep -i "crash\|exception\|restart"