Samsung Mobile Devices SIMalliance Toolbox Browser (S@T Browser) Remote Command Execution and Information Disclosure (CVE-2019-16256, Simjacker)
Executive & SecOps Summary
SECOPS ASSESSMENTSome Samsung mobile devices utilizing UICC (SIM cards) that include the SIMalliance Toolbox Browser (S@T Browser)
Remote attackers can retrieve sensitive location and IMEI information, or execute arbitrary SIM Toolkit (STK) commands via specially crafted SMS messages without user interaction
Apply the latest carrier and manufacturer OTA firmware updates, and request a replacement SIM card with S@T Browser security filtering enabled
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
This vulnerability requires mitigation at both the carrier network level and the device firmware level. Ensure your Android OS and carrier settings are fully updated.
# Verify the current Android OS build and carrier configuration via ADB
adb shell getprop ro.build.version.release
adb shell getprop gsm.sim.operator.numeric2. Temporary Workaround & Hardening Configuration
Coordinate with your mobile network operator (MNO) to block binary/OTA SMS messages containing S@T Browser command structures at the network level. For enterprise fleets, utilize MDM solutions to monitor unauthorized background SMS activities.
# Monitor background SMS delivery and STK command execution events via ADB
adb logcat | grep -Ei 'SMS_DELIVER|STK_CMD|SimPhonebook'3. Log Audit & IoC Verification Commands
Audit device logs to detect anomalous SIM Toolkit (STK) service behaviors or unauthorized background SMS transmissions.
# Extract and filter device logs for suspicious StkService activities
adb logcat -d | grep -i 'StkService'Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability, widely known as 'Simjacker', is a critical mobile network-based security flaw. It originates from a design defect in the SIMalliance Toolbox Browser (S@T Browser) application embedded on the UICC (SIM card) of certain Samsung mobile devices. The S@T Browser acts as an agent to execute SIM Toolkit (STK) instructions for carrier services, but it fails to properly validate and authenticate incoming SMS-based command requests.
2. Exploitation Mechanics & Attack Scenario
An attacker sends a specially crafted binary SMS (OTA SMS) containing specific SIM Toolkit (STK) instructions to the target device's phone number. Upon receipt, the mobile device bypasses user notification and forwards the payload directly to the S@T Browser on the UICC card. The S@T Browser executes the instructions, retrieves sensitive telemetry such as Cell ID (location data) and IMEI, and silently transmits this data back to the attacker via an outbound SMS.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 and its inclusion in the CISA KEV catalog, this vulnerability poses an active and severe threat. It enables zero-click, silent tracking of corporate personnel and device identification harvesting. Furthermore, attackers can leverage STK commands to initiate phone calls, redirect web browsers to malicious sites, or subscribe to premium services, leading to potential espionage and financial loss.
Official Vendor Advisories & References
Some Samsung devices include the SIMalliance Toolbox Browser (aka S@T Browser) on the UICC, which might allow remote attackers to retrieve location and IMEI information, or retrieve other data or execute certain commands, via SIM Toolkit (STK) instructions in an SMS message, aka Simjacker.
Frequently Asked SecOps Questions (CVE-2019-16256)
FAQQ1. How critical is CVE-2019-16256 and is it actively exploited in the wild?
CVE-2019-16256 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 5.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2019-16256?
Primary impacted vendors include samsung across samsung mobile devices, uicc. Scope summary: Certain Samsung mobile devices operating with UICC (SIM cards) that have the SIMalliance Toolbox Browser (S@T Browser) enabled
Q3. What temporary mitigations or workarounds exist for CVE-2019-16256 before patching?
[Mitigation] Apply the latest carrier and manufacturer OTA firmware updates, and request a replacement SIM card with S@T Browser security filtering enabled Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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