CVE-2018-18559 in Linux
Summary
by MITRE
In the Linux kernel through 4.19, a use-after-free can occur due to a race condition between fanout_add from setsockopt and bind on an AF_PACKET socket. This issue exists because of the 15fe076edea787807a7cdc168df832544b58eba6 incomplete fix for a race condition. The code mishandles a certain multithreaded case involving a packet_do_bind unregister action followed by a packet_notifier register action. Later, packet_release operates on only one of the two applicable linked lists. The attacker can achieve Program Counter control.
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Analysis
by VulDB Data Team • 05/30/2023
The vulnerability described in CVE-2018-18559 represents a critical use-after-free flaw in the Linux kernel version 4.19 and earlier, specifically affecting the packet socket implementation within the AF_PACKET family. This issue stems from an inadequate race condition fix introduced in commit 15fe076edea787807a7cdc168df832544b58eba6, which failed to properly address all multithreaded scenarios involving socket operations. The flaw manifests when concurrent execution of fanout_add through setsockopt and bind operations on AF_PACKET sockets creates a window where memory management becomes inconsistent. The root cause involves improper handling of a specific threading scenario where packet_do_bind performs an unregister action followed by a packet_notifier register action, creating a temporal gap in memory reference management.
The technical exploitation of this vulnerability occurs through a race condition that allows attackers to manipulate the kernel's memory management during socket binding operations. When fanout_add and bind operations execute concurrently, the kernel's packet socket subsystem fails to maintain proper synchronization between the unregister and register actions, leading to a situation where freed memory can be accessed again through a use-after-free condition. This particular flaw operates within the packet socket layer of the Linux networking stack, specifically affecting how the kernel manages linked list structures during socket lifecycle operations. The incomplete fix referenced in the commit hash demonstrates that previous attempts to resolve similar race conditions were insufficient, leaving the system vulnerable to exploitation through carefully crafted concurrent socket operations.
The operational impact of this vulnerability extends beyond simple memory corruption, as it provides attackers with the capability to achieve program counter control, making it a severe privilege escalation vector. The use-after-free condition allows for arbitrary code execution within kernel space, potentially enabling attackers to gain root privileges or execute malicious code with kernel-level permissions. This represents a significant threat to system integrity and security, as kernel-level exploits are particularly dangerous due to their ability to bypass user-space security mechanisms and operate with the highest privileges. The vulnerability affects systems running Linux kernel versions up to 4.19, making it a widespread concern for organizations maintaining older kernel versions.
Mitigation strategies for CVE-2018-18559 require immediate kernel updates to versions that properly address the race condition and memory management issues. System administrators should prioritize patching affected systems and ensure that all kernel components are updated to versions that contain the complete fix for this vulnerability. Additionally, monitoring for suspicious socket operations and implementing network segmentation can help reduce the attack surface, though these measures do not address the underlying kernel flaw. Organizations should also consider implementing kernel hardening measures such as stack canaries, address space layout randomization, and other exploit mitigation techniques to reduce the effectiveness of potential exploitation attempts. This vulnerability aligns with CWE-416, which covers use-after-free conditions, and falls under ATT&CK technique T1068, which addresses exploit for privilege escalation through kernel vulnerabilities. The flaw demonstrates the complexity of race condition management in kernel code and the critical importance of thorough testing for concurrent operations in security-sensitive systems.