USB Device Handler

The USB Device Handler is a KubeArmor module that provides audit and enforcement capabilities for USB devices at the host level. It allows administrators to define fine-grained host security policies that control USB device access based on their class, subclass, protocol, and level.

To enable USB device enforcement, use the enableUSBDeviceHandler flag.

Note that the USB Device Handler requires host policies to be enabled as well. It operates only with KubeArmor host policies.

You can define policies that enforce actions on specific USB devices by their hardware classification. See the policy spec here.

Working

The USB Device Handler works by:

1. Listening to kernel uevents via a Netlink socket for USB device attachments and removals.
2. When a USB device is attached, it matches the device against the currently applied host policies.
3. The most specific matching policy is selected and its action (Allow, Audit, or Block) is enforced.
4. Enforcement is achieved through sysfs-based USB authorization, by modifying the device configuration under /sys/bus/usb/devices/.

Policy Handling

The handler maintains an ordered list of rules, sorted by their specificity. Specificity is determined by the number of defined fields among:

• class
• subclass
• protocol
• level

Specificity Rules

• Each defined property increases the rule’s specificity.
• Rules are sorted in decreasing order of specificity.
• If multiple rules have the same specificity, action priority decides which one is used: Block > Audit > Allow

For example, consider these three host policies:

#	Class	Sub Class	Protocol	Level	Action
1	8	6	80	2	Allow
2	8	6	80	2	Block
3	8	6	-	2	Audit

After evaluation, the handler will generate the following internal rules:

#	Class (100)	Sub Class (10)	Protocol (1)	Level (100)	Action	Specificity
1	8	6	80	2	Block	211
2	8	6	-	2	Audit	210

Note that the Allow rule (policy #1) was replaced by the Block rule (policy #2) because they target the same device attributes and Block has higher priority.

Enforcement Mode

If there is at least one Allow rule, the handler operates in Allowlist Mode. Devices not matching any policy will have their behavior decided by the host default device posture. It can be audit or block (default is audit).

You can configure this using the hostDefaultDevicePosture flag.

Supported USB Classes

Decimal	Hex	Class Name	Description
1	0x01	AUDIO	Audio devices
2	0x02	COMMUNICATION-CDC	Communications & CDC Control
3	0x03	HID	Human Interface Devices (keyboard, mouse etc.)
5	0x05	PHYSICAL	Physical devices
6	0x06	IMAGE	Cameras, scanners
7	0x07	PRINTER	Printers
8	0x08	MASS-STORAGE	Storage devices (flash drives, external HDDs, etc.)
9	0x09	HUB	Hubs
10	0x0A	CDC-DATA	CDC Data interface
11	0x0B	SMART-CARD	Smart Card readers
13	0x0D	CONTENT-SECURITY	Content security devices
14	0x0E	VIDEO	Video devices (Webcams, capture cards)
15	0x0F	PERSONAL-HEALTHCARE	Healthcare/medical devices
16	0x10	AUDIO/VIDEO	Audio/Video devices
17	0x11	BILLBOARD	Billboard devices
18	0x12	TYPE-C-BRIDGE	Type-C bridge devices
19	0x13	BULK-DISPLAY	Bulk Display Protocol devices
20	0x14	MCTP	MCTP over USB protocol endpoint
60	0x3C	I3C	I3C over USB devices
220	0xDC	DIAGNOSTIC	Diagnostic devices
224	0xE0	WIRELESS-CONTROLLER	Wireless controllers (Bluetooth, WiFi adapters)
239	0xEF	MISCELLANEOUS	Miscellaneous devices
254	0xFE	APPLICATION-SPECIFIC	Application-defined class
255	0xFF	VENDOR-SPECIFIC	Vendor-defined proprietary class

As defined by usb.org.

Policy examples

• Keyboard

  apiVersion: security.kubearmor.com/v1
  kind: KubeArmorHostPolicy
  metadata:
    name: hsp-block-keybd
  spec:
    nodeSelector:
      matchLabels:
        kubernetes.io/hostname: aryan
    severity: 5
    device:
      matchDevice:
      - class: HID
        subClass: 1
        protocol: 1
    action: Block
  

  The above policy will block USB keyboards attached at any level to the host with hostname aryan

• Mouse

  apiVersion: security.kubearmor.com/v1
  kind: KubeArmorHostPolicy
  metadata:
  name: hsp-audit-mouse
  spec:
  nodeSelector:
      matchLabels:
      kubernetes.io/hostname: aryan
  severity: 5
  device:
      matchDevice:
      - class: "0x3"
      subClass: 1
      protocol: 2
      level: 1
  action: Audit
  

  The above policy will audit USB mice attached directly to the host with hostname aryan

Known Limitation: Composite USB Devices (Mouse + Keyboard)

When a composite USB device that controls both mouse and keyboard is connected, and a KubeArmor policy is applied to block either one of them (for example, the mouse or the keyboard interface), both stop functioning. In sysfs although, only the targeted interface is deauthorized according to the policy. But the entire composite device becomes unavailable to the system.