CVE-2017-18208 in Linux
Summary
by MITRE
The madvise_willneed function in mm/madvise.c in the Linux kernel before 4.14.4 allows local users to cause a denial of service (infinite loop) by triggering use of MADVISE_WILLNEED for a DAX mapping.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2017-18208 represents a critical denial of service flaw within the Linux kernel's memory management subsystem. This issue specifically affects the madvise_willneed function located in the mm/madvise.c file, which is responsible for handling memory advice operations. The vulnerability arises when local users exploit a particular combination of memory management operations that leads to an infinite loop condition within the kernel's memory subsystem. The flaw manifests when MADVISE_WILLNEED advice is applied to Direct Access (DAX) mappings, creating a scenario where kernel threads become trapped in an endless processing cycle that consumes system resources and effectively renders the system unresponsive.
The technical root cause of this vulnerability stems from inadequate boundary checking and loop termination conditions within the kernel's memory management code. When the madvise_willneed function processes DAX mappings, it fails to properly validate the memory mapping state or implement proper loop exit mechanisms. This allows malicious local users to craft specific memory access patterns that cause the kernel to repeatedly process the same memory advisory operation without proper termination conditions. The vulnerability is particularly dangerous because it operates entirely within the kernel space, making it difficult to detect and mitigate from user-space applications. The infinite loop consumes CPU cycles and memory resources, eventually leading to system instability and complete denial of service for legitimate system operations.
From an operational perspective, this vulnerability poses significant risks to Linux systems that utilize DAX mappings for high-performance storage operations. DAX mappings are commonly employed in databases, high-frequency trading systems, and other applications requiring direct memory access to storage devices. The impact extends beyond simple system crashes, as the infinite loop can persist until system reboot, potentially causing extended downtime for critical infrastructure. Attackers can exploit this vulnerability with minimal privileges, making it particularly dangerous for multi-tenant environments or systems where user isolation is not properly enforced. The vulnerability affects systems running Linux kernel versions prior to 4.14.4, representing a substantial attack surface across numerous enterprise and cloud environments that may not have been updated to the patched kernel versions.
The remediation strategy for CVE-2017-18208 involves immediate kernel version updates to 4.14.4 or later, which contain the necessary patches to address the infinite loop condition in the madvise_willneed function. System administrators should prioritize patching critical infrastructure and production systems to prevent exploitation. Additionally, monitoring for unusual CPU usage patterns or memory consumption spikes can help detect exploitation attempts, though this approach is reactive rather than preventive. Organizations should implement comprehensive patch management processes to ensure timely deployment of kernel security updates, particularly for systems utilizing DAX mappings. The vulnerability aligns with CWE-835, which addresses infinite loops in software systems, and can be categorized under ATT&CK technique T1499.001 for denial of service attacks. Given the low privilege requirement for exploitation and the high impact on system availability, this vulnerability represents a significant threat to system integrity and should be treated with high priority in security assessment and remediation activities.