CVE-2021-43400 in BlueZ
Summary
by MITRE • 11/05/2021
An issue was discovered in gatt-database.c in BlueZ 5.61. A use-after-free can occur when a client disconnects during D-Bus processing of a WriteValue call.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/04/2025
The vulnerability identified as CVE-2021-43400 represents a critical use-after-free condition within the BlueZ Bluetooth protocol stack version 5.61. This flaw exists in the gatt-database.c component and specifically manifests during the processing of D-Bus WriteValue calls when a client disconnects from the Bluetooth service. The issue arises from improper memory management where freed memory locations are accessed after a client terminates the connection while a write operation is in progress, creating a potential avenue for arbitrary code execution or system instability.
The technical implementation of this vulnerability stems from the Bluetooth GATT (Generic Attribute Profile) database handling within BlueZ, which manages the storage and retrieval of Bluetooth service data. When a client initiates a WriteValue operation through the D-Bus interface and subsequently disconnects before the operation completes, the system fails to properly validate the connection state before accessing previously allocated memory structures. This memory management error creates a scenario where the freed memory can be reused by other processes, but the original code path attempts to access the freed memory location, resulting in undefined behavior that can be exploited by malicious actors.
From an operational perspective, this vulnerability presents significant security implications for any system running BlueZ 5.61 or earlier versions, particularly those that handle Bluetooth GATT services and D-Bus communication. The attack vector requires a connected client to initiate a WriteValue operation and then disconnect abruptly, making it potentially exploitable in scenarios where attackers can establish Bluetooth connections to target systems. The impact extends beyond simple system crashes to potentially allow privilege escalation or remote code execution depending on the system configuration and the attacker's level of access to the Bluetooth interface.
The vulnerability maps to CWE-416, which specifically addresses use-after-free errors in software implementations. This classification indicates that the flaw involves accessing memory after it has been freed, a common but dangerous pattern in memory management that can lead to various security outcomes including information disclosure, denial of service, or code execution. The ATT&CK framework categorizes this under T1059.007 for command and script injection, as exploitation could potentially lead to execution of malicious code through the compromised Bluetooth service. Organizations using BlueZ implementations should consider this vulnerability as part of their broader security posture assessment, particularly in environments where Bluetooth services are exposed to untrusted networks or where the system handles sensitive data through Bluetooth GATT profiles.
Mitigation strategies should focus on immediate patching of BlueZ to version 5.62 or later, which contains the necessary fixes for this memory management issue. System administrators should also implement network segmentation to limit Bluetooth service exposure and consider disabling unnecessary Bluetooth services when not actively required. Additionally, monitoring for unusual D-Bus activity patterns and implementing proper connection state validation can help detect potential exploitation attempts. The vulnerability highlights the importance of proper memory management practices in networked services and demonstrates how seemingly benign connection handling can create critical security weaknesses when not properly validated against race conditions and state transitions.