CVE-2021-3752 in Linux
Summary
by MITRE • 02/16/2022
A use-after-free flaw was found in the Linux kernel’s Bluetooth subsystem in the way user calls connect to the socket and disconnect simultaneously due to a race condition. This flaw allows a user to crash the system or escalate their privileges. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.
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Analysis
by VulDB Data Team • 02/19/2022
The vulnerability identified as CVE-2021-3752 represents a critical use-after-free flaw within the Linux kernel's Bluetooth subsystem that stems from improper handling of concurrent socket operations. This issue manifests when user processes simultaneously execute connect and disconnect operations on Bluetooth sockets, creating a race condition that exploits memory management weaknesses in the kernel's Bluetooth implementation. The flaw resides in the kernel's socket handling mechanisms where insufficient synchronization prevents proper memory deallocation and reuse, leading to potential privilege escalation or system crashes. The vulnerability is classified under CWE-416 as a use-after-free condition, which occurs when memory is freed and then accessed again, creating opportunities for malicious exploitation. The specific nature of this flaw places it within the ATT&CK framework under T1068 for exploit for privilege escalation and T1499 for endpoint denial of service, as the vulnerability can be leveraged to compromise system integrity and availability.
The technical implementation of this vulnerability exploits a race condition between the socket connection establishment and disconnection processes within the Bluetooth subsystem. When concurrent operations occur, the kernel's memory management fails to properly synchronize access to shared resources, allowing a user-space process to manipulate the timing of these operations to trigger memory corruption. The flaw specifically affects the socket layer where connection state transitions are not adequately protected against simultaneous access from multiple threads or processes. This creates a scenario where freed memory structures can be accessed or overwritten by subsequent operations, potentially allowing an attacker to control memory layout and execute arbitrary code with kernel privileges. The vulnerability's impact extends beyond simple system crashes to include privilege escalation capabilities, as successful exploitation can allow unprivileged users to gain root access to the system.
The operational impact of CVE-2021-3752 poses significant threats to system security and availability across Linux environments utilizing Bluetooth functionality. Organizations running affected kernel versions face potential compromise of their entire system infrastructure, as the vulnerability can be exploited by local users without requiring special privileges or network access. The confidentiality aspect of the threat is particularly concerning as successful exploitation can lead to unauthorized access to sensitive system data and potential information disclosure. Integrity is compromised through the possibility of code injection and privilege escalation, while availability is threatened through both system crashes and potential denial of service conditions that can render systems inoperable. The vulnerability affects all Linux kernel versions prior to the patch release, making it a widespread concern for system administrators and security teams managing enterprise environments. The flaw's exploitation requires minimal privileges and can be automated, making it particularly dangerous in environments where local user access is not properly restricted.
Mitigation strategies for CVE-2021-3752 must address both immediate patching requirements and broader system hardening measures. The primary recommendation involves applying kernel updates that contain the specific fixes for the Bluetooth subsystem race condition, ensuring that all systems are running patched versions of the Linux kernel. Organizations should prioritize patch management processes to minimize the window of exposure, particularly for systems with Bluetooth capabilities. Additional mitigations include implementing proper access controls to limit local user privileges, disabling Bluetooth functionality when not required, and monitoring system logs for potential exploitation attempts. Network segmentation and monitoring solutions should be employed to detect anomalous behavior that might indicate exploitation attempts. The vulnerability's nature suggests that system administrators should also consider implementing kernel lockdown mechanisms and restricting user capabilities through capabilities-based access controls. Regular security assessments and vulnerability scanning should be conducted to ensure that systems remain protected against similar race condition vulnerabilities in other kernel subsystems. Organizations should also review their incident response procedures to ensure readiness for potential exploitation scenarios that could compromise system integrity and availability.