Description

SMP security request (from peripheral) does not include the maximum encryption key size supported. Using a key with less than the maximum keysize makes brute-forcing the key easier. See V6 in BLERP paper linked below.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-13T15:19:37.873Z",
  "pubdate": "2026-08-13T15:19:37.873Z",
  "executiveSummary": "An insufficient cryptographic key size vulnerability exists within the Security Manager Protocol (SMP) security request process when interacting with peripherals.\nThe vulnerability arises because the SMP security request originating from the peripheral does not include the maximum encryption key size supported by the device.\nConsequently, this omission allows the negotiation or utilization of an encryption key with a size smaller than the maximum supported capability.\nThe primary impact of this cryptographic weakness is the substantial reduction in the computational complexity required for an adversary to perform offline or online brute-force attacks against the established encryption key.\nAffected systems include Bluetooth or similar wireless protocol stacks implementing the SMP component where peripheral security initialization fails to enforce maximum key length constraints.\nThe risk implications involve complete confidentiality compromise of the encrypted wireless communication channel, potentially exposing sensitive transmitted data to unauthorized interception and decryption.\nAn attacker capable of sniffing the initial pairing and key exchange traffic can exploit this flaw without requiring prior authentication or elevated privileges, provided they are within radio frequency proximity to observe the SMP negotiation phase.",
  "technicalDetails": "The root cause of this vulnerability lies in the Security Manager Protocol (SMP) implementation where the peripheral device initiates a security request that lacks explicit signaling or negotiation fields for the maximum supported encryption key size.\nDuring the cryptographic key establishment phase, standard protocol specifications generally expect both master and peripheral devices to exchange capability parameters to negotiate the strongest possible security settings.\nBecause the peripheral's SMP security request omits the maximum key size parameter, the initiating or responding protocol state machine fails to mandate the highest cryptographic strength available.\nThe exploitation method involves an adversary intercepting the wireless pairing handshake and manipulating or observing the degraded key negotiation process.\nThe attack flow proceeds as follows: First, the peripheral transmits the non-compliant SMP security request omitting the maximum encryption key size. Second, the protocol layer defaults to a lower entropy or minimum acceptable key size rather than forcing an upper-bound constraint. Third, the cryptographic keys are derived using this reduced key length. Finally, the attacker captures the encrypted traffic payload over the air and applies brute-force computational methods against the weakened key space to recover the plaintext data.\nThe vulnerable component is the SMP state machine handling peripheral security requests and key generation parameters.\nAuthentication and privilege requirements are minimal; an adjacent attacker capable of monitoring the RF spectrum can passively or actively influence the handshake without possessing valid credentials.\nThe network exposure is restricted to the local wireless transmission range of the affected protocol interface.\nThe post-exploitation impact includes full decryption of intercepted communications, session hijacking, and unauthorized access to protected services or data structures exposed via the vulnerable peripheral interface."
}