CVE-2020-25670 in Linux
Summary
by MITRE • 05/26/2021
A vulnerability was found in Linux Kernel where refcount leak in llcp_sock_bind() causing use-after-free which might lead to privilege escalations.
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Analysis
by VulDB Data Team • 05/29/2021
The vulnerability identified as CVE-2020-25670 represents a critical security flaw within the Linux kernel that manifests as a reference count leak in the llcp_sock_bind() function. This issue specifically affects the Bluetooth Low Energy (BLE) communication stack and occurs within the Logical Link Control and Adaptation Protocol (LLCP) implementation. The flaw exists in the kernel's handling of socket binding operations and creates a scenario where memory management becomes corrupted due to improper reference counting mechanisms. When the llcp_sock_bind() function processes socket binding requests, it fails to correctly manage the reference count of socket objects, leading to a situation where a socket structure may be freed while still being referenced elsewhere in the system.
The technical exploitation of this vulnerability results in a use-after-free condition that fundamentally compromises memory safety within the kernel space. This type of vulnerability is particularly dangerous because it can be leveraged to execute arbitrary code with kernel privileges, potentially enabling full system compromise. The reference count leak occurs during the socket binding process when the kernel fails to properly decrement the reference counter for a socket object after it has been bound, allowing the object to be freed prematurely while other parts of the system may still attempt to access it. This mismanagement of reference counts creates a window where attackers can manipulate the freed memory to achieve privilege escalation. The vulnerability is classified under CWE-466 as "Return of Pointer Value Not Owned" and aligns with ATT&CK technique T1068 which covers "Local Privilege Escalation" through kernel exploits.
The operational impact of CVE-2020-25670 extends beyond simple privilege escalation to encompass potential system instability and complete compromise of affected systems. Systems running vulnerable kernel versions are at risk of unauthorized access and data breaches when exploited by malicious actors. The vulnerability affects all Linux distributions that incorporate kernel versions containing the flawed llcp_sock_bind() implementation, making it a widespread concern across enterprise and consumer environments. Attackers can exploit this flaw by crafting specific Bluetooth communication patterns that trigger the socket binding process, thereby initiating the reference count leak and subsequent use-after-free condition. The exploitation requires minimal privileges and can be performed through legitimate Bluetooth communication channels, making detection difficult and increasing the attack surface significantly.
Mitigation strategies for CVE-2020-25670 primarily involve applying kernel updates and patches from trusted sources to address the reference counting implementation flaw. System administrators should prioritize patching affected kernel versions and ensure that all Bluetooth-related components are updated to prevent exploitation. Organizations should implement monitoring systems to detect anomalous Bluetooth communication patterns that may indicate exploitation attempts. The vulnerability highlights the importance of proper memory management practices in kernel code and underscores the need for comprehensive testing of reference counting mechanisms in security-critical subsystems. Additionally, implementing network segmentation and access controls can help limit the potential impact of successful exploitation attempts. Regular security audits of kernel components and adherence to secure coding practices, particularly regarding memory management and reference counting, are essential preventive measures that align with industry best practices for kernel security hardening.