CVE-2025-39889
📋 TL;DR
The Linux kernel's Bluetooth L2CAP implementation fails to validate encryption key size on incoming connections, allowing connections with insufficient key sizes when Security Mode 4 Level 4 requires 16-byte keys. This affects Linux systems with Bluetooth functionality enabled, potentially exposing Bluetooth communications to weaker encryption than configured.
💻 Affected Systems
- Linux kernel
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Attackers could establish Bluetooth connections with weak encryption keys (1-15 bytes instead of required 16 bytes), potentially enabling decryption of Bluetooth communications or man-in-the-middle attacks.
Likely Case
Bluetooth devices could connect with weaker-than-expected encryption, reducing the security of Bluetooth communications below the configured security level.
If Mitigated
With proper network segmentation and Bluetooth usage policies, impact is limited to Bluetooth communication channels only.
🎯 Exploit Status
Exploitation requires physical proximity and Bluetooth pairing/connection attempts. Demonstrated in PTS test case but no public exploit code known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel trees (commits referenced in CVE)
Vendor Advisory: https://git.kernel.org/stable/c/24b2cdfc16e9bd6ab3d03b8e01c590755bd3141f
Restart Required: No
Instructions:
1. Update Linux kernel to patched version from your distribution's repositories. 2. For custom kernels, apply commits from stable kernel tree. 3. Rebuild and install kernel if compiling from source.
🔧 Temporary Workarounds
Disable Bluetooth
allDisable Bluetooth functionality if not required
sudo systemctl stop bluetooth
sudo systemctl disable bluetooth
sudo rfkill block bluetooth
Use lower security mode
allConfigure Bluetooth to use Security Mode 4 Level 3 or lower if 16-byte key requirement is not needed
🧯 If You Can't Patch
- Disable Bluetooth on critical systems
- Implement network segmentation to isolate Bluetooth devices from sensitive networks
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if Bluetooth is enabled: 'uname -r' and 'systemctl status bluetooth'Check Version:
uname -rVerify Fix Applied:
Verify kernel version is updated and check Bluetooth connection logs for proper key size validation📡 Detection & Monitoring
Log Indicators:
- Bluetooth connection attempts with non-16-byte keys
- HCI logs showing key size mismatches
- L2CAP connection responses without security validation
Network Indicators:
- Bluetooth pairing attempts from unknown devices
- Unusual Bluetooth traffic patterns
SIEM Query:
bluetooth AND (key_size < 16 OR security_mode:4)🔗 References
- https://git.kernel.org/stable/c/24b2cdfc16e9bd6ab3d03b8e01c590755bd3141f
- https://git.kernel.org/stable/c/522e9ed157e3c21b4dd623c79967f72c21e45b78
- https://git.kernel.org/stable/c/9e3114958d87ea88383cbbf38c89e04b8ea1bce5
- https://git.kernel.org/stable/c/c6d527bbd3d3896375079f5dbc8b7f96734a3ba5
- https://git.kernel.org/stable/c/d49798ecd26e0ee7995a7fc1e90ca5cd9b4402d6
- https://git.kernel.org/stable/c/d4ca2fd218caafbf50e3343ba1260c6a23b5676a
- https://git.kernel.org/stable/c/ed503d340a501e414114ddc614a3aae4f6e9eae2
