Packet forging/injection attacks
BR/EDR
BLE
A packet injection attack consists of deliberately sending altered or crafted data packets to manipulate or disrupt the normal operation of connected devices. This is possible when there is no mechanism to verify that a packet is correctly formatted or originates from a legitimate device.
If an application implements custom security mechanisms and uses cryptography for a specific service, these application layer controls must be sufficient to prevent packet forging and injection attacks. Otherwise, despite implementing application level security, those protections may be bypassed.
Description
The procedure consists on studying and analyzing if the selected encryption methods are secure against packet forging and packet injection attacks.
This control is considered satisfactory when it is verified that the mechanism for generating a valid packet is not so trivial that it allows the creation of new packets without knowledge of the encryption key for the packet.
Related resources
To check this control, the following resources may be useful:
| ID | Description |
|---|---|
| BSAM-RES-04 | Bluetooth connections sniffing |
| BSAM-RES-05 | Capture of a Bluetooth connection |
Example case
During an audit, a device with custom application layer encryption is found. Particularly, an user is able to set a secret password in the device that cyphers the traffic at application layer.
Data packets exchanged with the device include a PDU that contains a sequence number to avoid replay attacks, as in BSAM-AP-05 (Replay attacks). This number gets incremented each time a packet is sent and it is checked that the new number is greater than the latest record in the device. The PDU also contains a CRC32 field to verify the integrity of the packet.
Packets are encrypted using an stream cypher. This means that a pseudo-random stream is generated and xored to the original packet.
In this scenario, an attacker can captura an encrypted message c for a an unknown plaintext m. The attacker can compute an encrypted message c’ = c ⊕ (Δ, CRC(Δ)) that will correctly decrypt to a message m’ = m ⊕ Δ . If the attacker uses the Δ changes to modify the sequence number part of the message, it is able to reinject packets back to the device without knowing its contents.
