Bug 1960009 (CVE-2020-26557) - CVE-2020-26557 kernel: predictable Authvalue in Bluetooth Mesh Provisioning Leads to MITM
Summary: CVE-2020-26557 kernel: predictable Authvalue in Bluetooth Mesh Provisioning L...
Keywords:
Status: NEW
Alias: CVE-2020-26557
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Nobody
QA Contact:
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Depends On: 1969609 1969610 1969618
Blocks: 1969593
TreeView+ depends on / blocked
 
Reported: 2021-05-12 19:11 UTC by Guilherme de Almeida Suckevicz
Modified: 2023-09-19 14:13 UTC (History)
45 users (show)

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A flaw was found in the Linux kernel’s Bluetooth Mesh Profile implementation. The Mesh Provisioning procedure has a vulnerability that allows an attacker observing or taking part in the provisioning to brute force the AuthValue if it has a fixed value or is selected predictably or with low entropy. If successful, an attacker can identify the AuthValue and authenticate to both the Provisioner and provisioned devices, allowing a Man-in-the-Middle (MITM) attack on a future provisioning attempt with the same AuthValue. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.
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Description Guilherme de Almeida Suckevicz 2021-05-12 19:11:46 UTC 
The Bluetooth Mesh Profile Specification versions 1.0 and 1.0.1 Mesh Provisioning procedure could allow an attacker observing or taking part in the provisioning to brute force the AuthValue if has a fixed value or is selected predictably or with low entropy. If successful, an attacker may be able to identify the AuthValue and authenticate to both the Provisioner and provisioned devices, permitting a MITM attack on a future provisioning attempt with the same AuthValue.
Comment 3 Rohit Keshri 2021-05-16 18:03:37 UTC 
Mitigation:

It is recommended for devices to use AuthValues containing the maximum entropy permitted (128-bits) and randomly select a new AuthValue using a secure random number generator with each new provisioning attempt.  A large entropy helps ensure that a brute-force of the AuthValue, even a static AuthValue, cannot normally be completed in a reasonable time.
Comment 18 Rohit Keshri 2021-06-08 18:40:46 UTC 
Created bluez tracking bugs for this issue:

Affects: fedora-all [bug 1969618]
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