CVE-2018-6927 in Linux
Summary
by MITRE
The futex_requeue function in kernel/futex.c in the Linux kernel before 4.14.15 might allow attackers to cause a denial of service (integer overflow) or possibly have unspecified other impact by triggering a negative wake or requeue value.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2018-6927 resides within the Linux kernel's futex_requeue function located in kernel/futex.c, representing a critical flaw that affects kernel versions prior to 4.14.15. This issue manifests as an integer overflow condition that can be exploited to cause system instability or potentially enable more severe security implications. The vulnerability specifically occurs when the futex subsystem processes wake or requeue operations, creating a scenario where negative values can be improperly handled within the kernel's synchronization mechanisms.
The technical flaw stems from inadequate input validation and boundary checking within the futex_requeue function, which is responsible for managing the requeueing of waiters in the futex (fast userspace mutex) subsystem. When an attacker can manipulate the parameters passed to this function, particularly those controlling the number of threads to wake or requeue, the system can encounter integer overflow conditions. This occurs because the function fails to properly validate that the wake or requeue values remain within acceptable positive integer ranges, allowing for negative values to be processed. The vulnerability is categorized under CWE-191 Integer Underflow (Wrap or Wraparound) which directly relates to the improper handling of negative integer values in kernel space operations.
The operational impact of this vulnerability extends beyond simple denial of service conditions, though DoS remains the primary concern. An attacker who can successfully trigger this condition can cause the kernel to enter an undefined state where it may crash or become unresponsive, effectively rendering the system unavailable to legitimate users. The potential for unspecified other impacts suggests that this integer overflow could potentially be leveraged to escalate privileges or bypass security controls, though the exact vector for such exploitation requires further analysis. The futex subsystem is fundamental to Linux kernel operations, handling synchronization primitives that are used extensively throughout the operating system, making this vulnerability particularly dangerous as it can affect multiple kernel components simultaneously.
Mitigation strategies for CVE-2018-6927 primarily focus on kernel version updates, as the issue has been resolved in kernel versions 4.14.15 and later. System administrators should prioritize patching affected systems, particularly those running kernel versions between 2.6.22 and 4.14.14, as these are most vulnerable to exploitation. Additionally, implementing proper input validation and boundary checking in kernel modules that interact with futex operations can provide defense-in-depth measures. Monitoring for unusual patterns in system calls related to futex operations may also help detect potential exploitation attempts. From an ATT&CK perspective, this vulnerability maps to T1499.004, specifically the technique of Network Denial of Service, as the primary impact is system unavailability, though potential privilege escalation pathways should be investigated through proper security auditing and kernel hardening measures.