CVE-2025-3885 – This vulnerability allows attackers within Blue... (How to Fix)

📋 TL;DR

This vulnerability allows attackers within Bluetooth range to crash Harman Becker MGU21 infotainment systems by sending malformed Bluetooth frames. No authentication is required, making any nearby device with Bluetooth capability a potential threat vector. Affected systems are vehicles equipped with vulnerable MGU21 units using the BCM89359 chipset.

💻 Affected Systems

Products:

Harman Becker MGU21 Automotive Infotainment System

Versions: All versions using BCM89359 chipset with vulnerable Bluetooth stack

Operating Systems: Embedded automotive OS

Default Config Vulnerable: ⚠️ Yes

Notes: Vulnerability exists in Bluetooth stack implementation on BCM89359 chipset. Requires Bluetooth to be enabled and in discoverable/connectable mode.

📦 What is this software?

Harman Mgu21 Firmware by Samsung

View all CVEs affecting Harman Mgu21 Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system crash requiring vehicle restart, potentially disabling critical infotainment functions including navigation, emergency calling, and vehicle status displays while driving.

🟠

Likely Case

Temporary denial of service affecting Bluetooth connectivity and infotainment functions until system reboot, disrupting media playback and hands-free calling.

🟢

If Mitigated

Limited impact with Bluetooth disabled or physical isolation from attackers, though core vehicle functions remain unaffected.

🌐 Internet-Facing: LOW - Attack requires physical proximity via Bluetooth, not internet connectivity.

🏢 Internal Only: MEDIUM - Attack requires proximity but no authentication, making any nearby Bluetooth device a potential threat.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Attack requires Bluetooth proximity but no special equipment beyond standard Bluetooth-capable device. ZDI advisory suggests exploit is straightforward.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Unknown

Vendor Advisory: Not publicly available

Restart Required: Yes

Instructions:

1. Contact Harman/vehicle manufacturer for firmware updates
2. Schedule service appointment at authorized dealership
3. Apply firmware update via diagnostic interface
4. Verify Bluetooth functionality post-update

🔧 Temporary Workarounds

Disable Bluetooth

all

Turn off Bluetooth functionality to prevent exploitation

Navigate to vehicle settings > Connectivity > Bluetooth > Turn OFF

Enable Pairing Mode Only When Needed

all

Set Bluetooth to non-discoverable mode and only enable pairing briefly

Settings > Bluetooth > Visibility > Hidden/Non-discoverable

🧯 If You Can't Patch

Physically isolate vehicle from untrusted Bluetooth devices when parked
Use wired connections for media playback instead of Bluetooth

🔍 How to Verify

Check if Vulnerable:

Check vehicle infotainment system model and firmware version against manufacturer advisories

Check Version:

Navigate to: Settings > System Information > Software Version

Verify Fix Applied:

Verify firmware version has been updated and test Bluetooth functionality with known good devices

📡 Detection & Monitoring

Log Indicators:

Bluetooth stack crashes
Unexpected Bluetooth disconnections
System reboot events

Network Indicators:

Malformed Bluetooth frames from unknown MAC addresses
Excessive Bluetooth connection attempts

SIEM Query:

Not applicable for automotive embedded systems

📊 Metadata

CVE ID: CVE-2025-3885

CVSS v3 Score: 6.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-20

EPSS Score: 0.05% exploit probability (16.6th percentile)

Published: May 22, 2025

Last Updated: August 15, 2025

🔗 References

https://www.zerodayinitiative.com/advisories/ZDI-25-251/ Third Party Advisory

📤 Share & Export

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