CVE-2017-18261 in Linux
Summary
by MITRE
The arch_timer_reg_read_stable macro in arch/arm64/include/asm/arch_timer.h in the Linux kernel before 4.13 allows local users to cause a denial of service (infinite recursion) by writing to a file under /sys/kernel/debug in certain circumstances, as demonstrated by a scenario involving debugfs, ftrace, PREEMPT_TRACER, and FUNCTION_GRAPH_TRACER.
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Analysis
by VulDB Data Team • 03/03/2023
The vulnerability CVE-2017-18261 represents a critical design flaw in the Linux kernel's ARM64 architecture implementation that enables local privilege escalation through denial of service conditions. This issue resides within the arch_timer_reg_read_stable macro located in arch/arm64/include/asm/arch_timer.h, which forms part of the kernel's timer subsystem responsible for handling architectural timer operations on ARM64 processors. The flaw specifically manifests when local users manipulate files within the /sys/kernel/debug filesystem, creating a scenario where recursive function calls can occur without proper termination conditions.
The technical execution of this vulnerability involves exploiting the interaction between debugfs filesystem operations and the kernel's tracing infrastructure. When users write to specific debugfs entries while the system is configured with ftrace enabled alongside PREEMPT_TRACER and FUNCTION_GRAPH_TRACER options, the arch_timer_reg_read_stable macro becomes susceptible to infinite recursion patterns. This occurs because the macro's implementation fails to properly validate or limit recursive calls during timer register reads, particularly when tracing mechanisms are active and monitoring kernel operations. The vulnerability is categorized under CWE-674, which addresses "Uncontrolled Recursion" in software systems.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can effectively render the affected system unstable and unresponsive to legitimate operations. When infinite recursion occurs within kernel space, the system may experience complete lockups where the processor becomes trapped in recursive function calls, preventing normal system operations from proceeding. This condition can persist until manual intervention occurs through system reboot or kernel panic detection mechanisms. The vulnerability affects Linux kernel versions prior to 4.13, making it particularly concerning for systems running older kernel versions that may not have received the necessary patches.
Mitigation strategies for CVE-2017-18261 primarily focus on kernel version upgrades to 4.13 or later, which contain the necessary fixes to prevent the recursive call patterns that lead to system instability. System administrators should also consider disabling unnecessary debugfs interfaces and tracing mechanisms when not actively required for debugging purposes. The implementation of proper input validation and recursion depth monitoring within kernel timer subsystems provides additional protective measures. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service through kernel exploitation, specifically targeting the kernel's timer subsystem and debugging interfaces. Organizations should also implement comprehensive monitoring for unusual patterns in debugfs file operations and kernel tracing configurations to detect potential exploitation attempts.