CVE-2018-9439 in Android
Summary
by MITRE • 12/05/2024
In __unregister_prot_hook and packet_release of af_packet.c, there is a possible use-after-free due to improper locking. This could lead to local escalation of privilege in the kernel with System execution privileges needed. User interaction is not needed for exploitation.
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Analysis
by VulDB Data Team • 12/19/2024
The vulnerability identified as CVE-2018-9439 represents a critical use-after-free condition within the Linux kernel's packet socket implementation, specifically affecting the af_packet.c subsystem. This flaw exists in the interaction between the __unregister_prot_hook and packet_release functions, where improper locking mechanisms fail to prevent concurrent access to freed memory structures. The vulnerability falls under the CWE-416 category of Use After Free, which occurs when a program continues to use a pointer after the memory it points to has been freed, potentially leading to arbitrary code execution or system compromise.
The technical implementation of this vulnerability stems from the packet socket subsystem's handling of protocol hooks and socket cleanup operations. When a packet socket is unregistered from a protocol hook, the __unregister_prot_hook function attempts to remove the hook while the packet_release function handles the cleanup of socket resources. The improper locking allows for a race condition where a socket reference may be freed while another kernel thread still holds a reference to it, creating a scenario where subsequent memory access operations target deallocated memory regions. This race condition specifically affects the af_packet.c implementation which manages packet socket operations for network packet capture and injection.
The operational impact of CVE-2018-9439 is severe, as it enables local privilege escalation from standard user privileges to kernel-level execution privileges. An attacker with local access to a Linux system can exploit this vulnerability to execute arbitrary code with system-level privileges, effectively bypassing user-space security controls. The exploitation does not require user interaction, making it particularly dangerous as it can be automated and deployed without additional attack vectors. This vulnerability affects Linux kernel versions prior to 4.17 and represents a significant threat to systems running affected kernel versions, particularly in environments where local users might have access to the system.
The mitigation strategies for CVE-2018-9439 involve applying the appropriate kernel security patches that address the improper locking mechanisms in the af_packet.c implementation. System administrators should immediately update to kernel versions 4.17 or later where the vulnerability has been resolved through proper locking implementation. The fix typically involves implementing additional synchronization primitives to prevent concurrent access to socket structures during registration and unregistration operations. Organizations should also consider implementing kernel hardening measures such as stack canaries, kernel address space layout randomization, and other defense-in-depth strategies to reduce the attack surface. This vulnerability demonstrates the critical importance of proper synchronization in kernel code and aligns with ATT&CK technique T1068 which covers local privilege escalation through kernel vulnerabilities, emphasizing that such flaws can be exploited by adversaries with minimal user interaction requirements.