CVE-2020-26556 – This vulnerability in Bluetooth Mesh provisioni... (How to Fix)

Q: What is the severity of CVE-2020-26556?

CVE-2020-26556 has a CVSS score of 7.5 (HIGH). This vulnerability in Bluetooth Mesh provisioning allows a nearby attacker to brute-force the AuthValue during device pairing before the provisioning timeout. Successful exploitation permits unauthorized authentication and potential network access. It affects devices using Bluetooth Mesh profile 1.0 and 1.0.1 with insufficiently random AuthValues.

📋 TL;DR

This vulnerability in Bluetooth Mesh provisioning allows a nearby attacker to brute-force the AuthValue during device pairing before the provisioning timeout. Successful exploitation permits unauthorized authentication and potential network access. It affects devices using Bluetooth Mesh profile 1.0 and 1.0.1 with insufficiently random AuthValues.

💻 Affected Systems

Products:

Devices implementing Bluetooth Mesh profile

Versions: Bluetooth Mesh profile 1.0 and 1.0.1

Operating Systems: Any OS with vulnerable Bluetooth Mesh implementation

Default Config Vulnerable: ⚠️ Yes

Notes: Vulnerability depends on implementation quality of AuthValue generation and provisioning timeout settings.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attacker gains unauthorized access to Bluetooth Mesh network, enabling data interception, device impersonation, or network disruption.

🟠

Likely Case

Unauthorized device joins the mesh network, potentially enabling eavesdropping or limited network manipulation.

🟢

If Mitigated

With strong AuthValues and proper timeout settings, exploitation becomes computationally infeasible within the provisioning window.

🌐 Internet-Facing: LOW - Requires physical proximity to Bluetooth range, not internet-based exploitation.

🏢 Internal Only: MEDIUM - Physical access to Bluetooth range needed, but internal devices could be targeted by nearby attackers.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Requires proximity during provisioning, brute-force capability, and knowledge of Malleable Commitment attack.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Bluetooth Mesh profile 1.0.1 with proper implementations or updated versions

Vendor Advisory: https://www.bluetooth.com/learn-about-bluetooth/key-attributes/bluetooth-security/reporting-security/

Restart Required: Yes

Instructions:

1. Check with device manufacturer for firmware updates. 2. Apply Bluetooth Mesh profile updates. 3. Ensure AuthValue uses cryptographically secure random generation. 4. Implement proper provisioning timeout limits.

🔧 Temporary Workarounds

Increase AuthValue entropy

all

Ensure AuthValue uses cryptographically secure random number generation with sufficient entropy

Implementation-specific - consult device documentation

Reduce provisioning timeout

all

Shorten provisioning timeout window to limit brute-force opportunity

Implementation-specific - consult device documentation

🧯 If You Can't Patch

Disable Bluetooth Mesh provisioning in untrusted environments
Physically secure devices during provisioning to prevent nearby attacks

🔍 How to Verify

Check if Vulnerable:

Check Bluetooth Mesh profile version and implementation details from device manufacturer

Check Version:

Device-specific - consult manufacturer documentation for version checking

Verify Fix Applied:

Verify updated firmware implements secure AuthValue generation and proper timeout handling

📡 Detection & Monitoring

Log Indicators:

Multiple failed provisioning attempts from same device
Unusual provisioning activity patterns

Network Indicators:

Unexpected devices appearing in Bluetooth Mesh network
Unusual provisioning traffic

SIEM Query:

Search for Bluetooth Mesh provisioning failures exceeding normal thresholds

📊 Metadata

CVE ID: CVE-2020-26556

CVSS v3 Score: 7.5 (HIGH)

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

CWE: CWE-307

Published: May 24, 2021

Last Updated: November 21, 2024

🔗 References

https://kb.cert.org/vuls/id/799380 Third Party Advisory,US Government Resource
https://www.bluetooth.com/learn-about-bluetooth/key-attributes/bluetooth-security/reporting-security/ Vendor Advisory
https://www.kb.cert.org/vuls/id/799380 Third Party Advisory,US Government Resource
https://kb.cert.org/vuls/id/799380 Third Party Advisory,US Government Resource
https://www.bluetooth.com/learn-about-bluetooth/key-attributes/bluetooth-security/reporting-security/ Vendor Advisory
https://www.kb.cert.org/vuls/id/799380 Third Party Advisory,US Government Resource

📤 Share & Export

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