CVE-2018-17154 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.2-STABLE(r338987), 11.2-RELEASE-p4, and 11.1-RELEASE-p15, due to insufficient memory checking in the freebsd4_getfsstat system call, a NULL pointer dereference can occur. Unprivileged authenticated local users may be able to cause a denial of service.
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Analysis
by VulDB Data Team • 05/19/2023
The vulnerability identified as CVE-2018-17154 affects FreeBSD operating systems prior to specific release versions including 11.2-STABLE(r338987), 11.2-RELEASE-p4, and 11.1-RELEASE-p15. This issue stems from inadequate memory validation within the freebsd4_getfsstat system call implementation, creating a condition where a NULL pointer dereference can manifest when processing certain file system statistics requests. The flaw specifically impacts unprivileged authenticated local users who can exploit this weakness to trigger system instability.
The technical implementation of the vulnerability resides in the freebsd4_getfsstat system call which serves as a compatibility interface for older FreeBSD applications that expect the legacy file system statistics format. During normal operation, this system call retrieves file system information from the kernel's internal data structures and formats it for user-space consumption. However, insufficient validation occurs when processing memory allocations for the returned data structures, particularly when handling cases where certain file system entries may not be properly initialized or where memory allocation fails. This inadequate checking allows a malicious user to craft specific input parameters that cause the kernel to attempt to dereference a NULL pointer, leading to immediate system termination or panic.
From an operational perspective, this vulnerability represents a local denial of service condition that can be exploited by any authenticated user with access to the system. The impact extends beyond simple service disruption as the NULL pointer dereference typically results in a kernel panic, requiring system reboot to restore normal operation. This vulnerability is particularly concerning in multi-user environments where unprivileged users might have legitimate access to the system but could potentially cause service interruptions for other users or system administrators. The exploitability is relatively straightforward since it requires only local authentication and does not demand elevated privileges or complex attack vectors.
The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions in software implementations. Additionally, this weakness maps to ATT&CK technique T1499.004 which covers network disruption through resource exhaustion and system shutdown. The attack surface is limited to local system access but the potential for system-wide disruption makes it a significant concern for system administrators managing FreeBSD environments. The vulnerability demonstrates poor defensive programming practices where proper error handling and memory validation were not implemented within kernel space code paths.
Mitigation strategies for CVE-2018-17154 involve immediate deployment of the patched FreeBSD releases containing the fix for the freebsd4_getfsstat system call implementation. System administrators should prioritize upgrading to FreeBSD 11.2-RELEASE-p4, 11.1-RELEASE-p15, or newer stable releases that contain the necessary memory validation corrections. Organizations should also implement monitoring for unauthorized local access attempts and ensure that user accounts have appropriate privilege levels to minimize potential exploitation. Regular patch management procedures should be enforced to maintain systems at current security baselines. The fix implemented by FreeBSD developers corrects the memory allocation validation within the system call to properly handle edge cases and prevent NULL pointer dereference conditions.