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[FAQ] CC254x OAD: AES CTR crypto implementation vulnerability

Marie H
Guru 67811 points
Other Parts Discussed in Thread: CC2541, CC2540, BLE-STACK

Summary

In the CC254x OAD solution:

  • aesCrypt function in EBL/app/sbl_exec.c is used to encrypt the OAD image (64 bytes of data at a time)
  • imgCrypt function in BEM/app/bem_main.c is used to decrypt the OAD image

AES-CTR cryptographic function is used in both the encryption functions above. The cryptographic function implementation resets the AES-CTR counter to its initial value every 4 AES blocks (64-bytes), resulting in keystream repetition every 64-bytes. This vulnerability can potentially be used to decrypt a firmware image without having to recover the AES key.

CVSS base score: 8.1

CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H)

Affected products

  • CC2540/CC2541 BLE-Stack SDK v1.5.0 and earlier

Potentially Impacted features

  • The potential vulnerability can impact the OAD image encryption functionality.

Suggested actions

The following service-pack release addresses the potential vulnerability:

Customers of affected products should apply this service-pack and consider further system-level security measures as appropriate. Customers are solely responsible for the security of their products and are encouraged to assess the possible risk of any potential security vulnerability.

Source

We would like to thank researchers from COSIC, KU Leuven and imec for reporting this potential vulnerability to the TI Product Security Incident Response Team (PSIRT) and working toward a coordinated report.

 

 

 

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