CVE-2017-18241 in Linux
Summary
by MITRE
fs/f2fs/segment.c in the Linux kernel before 4.13 allows local users to cause a denial of service (NULL pointer dereference and panic) by using a noflush_merge option that triggers a NULL value for a flush_cmd_control data structure.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2017-18241 resides within the Linux kernel's F2FS (Flash-Friendly File System) implementation, specifically in the segment.c file. This flaw represents a critical NULL pointer dereference condition that can be exploited by local attackers to trigger a system panic and subsequent denial of service. The vulnerability affects Linux kernel versions prior to 4.13, making it a significant concern for systems running older kernel versions where patching may not be immediately available.
The technical root cause stems from improper handling of the flush_cmd_control data structure when the noflush_merge option is utilized. This option is designed to control how flush commands are merged during file system operations, but when improperly configured or invoked, it results in a NULL pointer being dereferenced. The flaw occurs during the segment management operations within F2FS where the system attempts to access a flush command control structure that has not been properly initialized or has been set to NULL. This NULL pointer dereference represents a classic software bug pattern that can be categorized under CWE-476, which specifically addresses NULL pointer dereference vulnerabilities.
The operational impact of this vulnerability extends beyond simple denial of service as it can lead to complete system crashes and potential data corruption. Local users with access to the system can exploit this condition to force the kernel into a panic state, effectively bringing the entire system down. This type of vulnerability is particularly dangerous in server environments where availability is critical, as it can be used to disrupt services without requiring external network access. The attack vector is straightforward and requires only local system access, making it a low-barrier exploit that can be leveraged by malicious insiders or compromised accounts.
From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service. The local execution requirement places it within the realm of privilege escalation tactics, as attackers can leverage this to gain more control over affected systems. The system crash behavior corresponds to the denial of service technique, where the attacker can disrupt normal system operations and potentially cause data loss or corruption. Organizations should consider this vulnerability as part of their broader security posture assessment, particularly when evaluating the risk of insider threats and the importance of maintaining current kernel versions.
Mitigation strategies for CVE-2017-18241 primarily focus on kernel version updates, as the vulnerability was resolved in Linux kernel version 4.13 and subsequent releases. System administrators should prioritize patching affected systems to ensure the latest kernel versions are deployed across their infrastructure. Additionally, monitoring systems should be configured to detect unusual kernel panic events or system crashes that might indicate exploitation attempts. The vulnerability also highlights the importance of proper input validation and null pointer checks in kernel code, serving as a reminder that even minor kernel subsystems can contain critical flaws that affect system stability. Organizations should implement regular kernel security assessments and maintain up-to-date security patches as part of their vulnerability management processes to prevent similar issues from occurring in other kernel components.