CVE-2025-5477

Executive Summary

CVE-2025-5477 is a critical heap-based buffer overflow vulnerability in the Bluetooth L2CAP protocol implementation of the Sony XAV-AX8500 in-car infotainment system. An attacker with network-adjacent access and the ability to pair a malicious Bluetooth device can trigger remote code execution (RCE) within the elysian-bt-service process. The vulnerability arises from improper validation of user-supplied data length before copying it to a heap buffer, leading to memory corruption and arbitrary code execution. With a CVSS score of 7.5, this flaw poses a significant risk to vehicle safety and user privacy, as exploitation could allow an attacker to take full control of the Bluetooth subsystem, potentially affecting other vehicle systems. No public proof-of-concept (PoC) or exploit code is currently available, and no official patch has been released by Sony.

Supply Chain & Package Security

This vulnerability is not related to any open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary embedded system (Sony XAV-AX8500) and its Bluetooth stack. No supply chain implications are present.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Attack Vector (AV): Adjacent Network – attacker must be within Bluetooth range.
• Attack Complexity (AC): Low – no special conditions required beyond pairing.
• Privileges Required (PR): None – no prior authentication needed.
• User Interaction (UI): Required – victim must accept pairing request.
• Scope (S): Unchanged – exploitation stays within the Bluetooth service.
• Confidentiality (C): High – potential data exfiltration from the device.
• Integrity (I): High – attacker can modify system state.
• Availability (A): High – crash or denial of service possible.

Threat Level: High. Exploitation requires only Bluetooth proximity and user interaction (pairing), making it feasible for targeted attacks in parking lots or drive-by scenarios.

Deep Dive & Mechanics

The vulnerability resides in the Bluetooth L2CAP (Logical Link Control and Adaptation Protocol) layer of the Sony XAV-AX8500. L2CAP is responsible for multiplexing data between higher-layer protocols (e.g., SDP, RFCOMM) and the lower-layer Baseband. The specific flaw is in the handling of incoming L2CAP packets: when a packet with a length field exceeding the allocated heap buffer size is received, the elysian-bt-service process copies the data without proper bounds checking, causing a heap-based buffer overflow.

Technical Details:

• Affected Component: elysian-bt-service – the proprietary Bluetooth service on the Sony XAV-AX8500.
• Root Cause: Lack of validation of the length field in L2CAP frames before memcpy or similar operation.
• Exploitation Prerequisites: Attacker must pair a malicious Bluetooth device with the target system. This requires the victim to accept a pairing request (user interaction).
• Impact: Successful exploitation allows arbitrary code execution in the context of elysian-bt-service, which runs with elevated privileges. This can lead to full compromise of the Bluetooth subsystem, enabling actions such as:
  • Injecting malicious audio or data streams.
  • Accessing stored contacts, call logs, or other sensitive data.
  • Potentially pivoting to other vehicle systems (e.g., CAN bus) if the service has such access.

Attack Flow:

1. Attacker sets up a Bluetooth device with a malicious L2CAP packet generator.
2. Victim pairs with the attacker’s device (e.g., via a fake “Sony” device name).
3. Attacker sends a crafted L2CAP packet with an oversized length field.
4. The elysian-bt-service copies the payload into a fixed-size heap buffer, causing overflow.
5. Attacker overwrites adjacent heap metadata or function pointers to gain code execution.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is inferred from the CVE description. The following pseudo-code illustrates the flaw:

Vulnerable Code (C-like):

void process_l2cap_packet(uint8_t *packet, uint16_t length) {
    uint8_t *buffer = malloc(256); // Fixed-size heap buffer
    if (buffer == NULL) return;
    // No length check before copy
    memcpy(buffer, packet, length); // Overflow if length > 256
    // ... process buffer
}

Patched Code (Hypothetical):

void process_l2cap_packet(uint8_t *packet, uint16_t length) {
    uint8_t *buffer = malloc(256);
    if (buffer == NULL) return;
    // Validate length before copy
    if (length > 256) {
        // Reject packet or truncate
        free(buffer);
        return;
    }
    memcpy(buffer, packet, length);
    // ... process buffer
}

The patch would add a bounds check to ensure length does not exceed the allocated buffer size.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• Target: Sony XAV-AX8500 head unit (or emulator if available).
• Attacker Machine: Linux with Bluetooth adapter (e.g., CSR dongle) and BlueZ stack.
• Tools: btlejack, scapy, custom Python script for L2CAP packet crafting.

Exploitation Steps:

1. Pairing: Use bluetoothctl to pair with the target device (requires user acceptance).
2. Craft Malicious L2CAP Packet: Use Scapy to create a packet with an oversized length field.

   from scapy.all import *
   # L2CAP header: length (2 bytes), CID (2 bytes)
   payload = b"A" * 512  # Overflow data
   l2cap_pkt = L2CAP_Hdr(len=512, cid=0x0001) / Raw(payload)
   # Send via L2CAP socket
   

3. Send Packet: Use a raw Bluetooth socket to send the packet to the target.

   # Example using l2ping (not directly exploitable, but for testing)
   l2ping -s 512 -c 1 <target_mac>
   

4. Trigger Overflow: The oversized packet causes heap corruption, leading to code execution.

Note: No public exploit code exists. The above is a conceptual approach.

Blue Team (Defensive)

Detection & Prevention:

• Network Monitoring: Monitor Bluetooth traffic for anomalous L2CAP packets with excessive length fields (>256 bytes).
• Host-Based Detection: On the head unit, monitor elysian-bt-service for crashes or abnormal memory access patterns.
• User Awareness: Educate users to only pair with trusted devices and reject unexpected pairing requests.
• Firmware Hardening: Implement input validation and bounds checking in the L2CAP handler.

Mitigation Steps:

• Disable Bluetooth when not in use.
• Use Bluetooth pairing with PIN code or passkey to reduce risk of unauthorized pairing.
• Apply firmware updates as soon as Sony releases a patch.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Bluetooth L2CAP packets with length field > 256 bytes.
  • Repeated pairing attempts from unknown devices.
• Host IOCs:
  • Crash logs from elysian-bt-service (e.g., segmentation faults).
  • Unexpected memory allocations in the Bluetooth heap.
  • Presence of shellcode or unusual processes spawned by elysian-bt-service.
• File IOCs:
  • Modified firmware binaries or configuration files in /etc/bluetooth/.
  • New files in /tmp/ or /var/run/ created by the exploited service.

Detection Engineering

YARA Rule

rule CVE_2025_5477_L2CAP_Overflow {
    meta:
        description = "Detects heap overflow attempts in Sony XAV-AX8500 L2CAP packets"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-5477"
    strings:
        $l2cap_header = { ?? ?? 00 01 } // L2CAP length + CID 0x0001
        $large_length = { 01 00 } // Length > 256 (0x0100)
    condition:
        $l2cap_header and $large_length
}

Sigma Rule

title: CVE-2025-5477 Bluetooth L2CAP Heap Overflow Attempt
id: 8a3f2c1d-5e7b-4a9f-8c6d-2e1f3a4b5c6d
status: experimental
description: Detects oversized L2CAP packets targeting Sony XAV-AX8500
author: Valters IT
logsource:
    product: linux
    service: bluetooth
detection:
    selection:
        - EventID: 1000  # Example: Bluetooth packet log
        - PacketLength: > 256
        - Protocol: L2CAP
    condition: selection
falsepositives:
    - Legitimate large L2CAP packets (rare)
level: high

Suricata Rule

alert bluetooth any any -> any any (msg:"CVE-2025-5477 L2CAP Heap Overflow Attempt"; content:"|00 01|"; offset:2; depth:2; byte_test:2,>,256,0; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Bluetooth on the Sony XAV-AX8500 if not required.
2. Avoid pairing with unknown or untrusted Bluetooth devices.
3. Monitor for any suspicious Bluetooth activity or crashes.

Long-Term Fix:

• Vendor Patch: Await an official firmware update from Sony that includes proper input validation in the L2CAP handler.
• Workaround: If a patch is not available, consider using a Bluetooth firewall or filtering device that blocks oversized packets.

Valters IT Recommendations:

• Implement a security policy for Bluetooth usage in vehicles.
• Regularly check for firmware updates from Sony.
• Use network segmentation to isolate the infotainment system from critical vehicle controls.

Report generated by Valters IT – DevSecOps & Cyber Threat Intelligence Division.