CVE-2015-8966 in Linux
Summary
by MITRE
arch/arm/kernel/sys_oabi-compat.c in the Linux kernel before 4.4 allows local users to gain privileges via a crafted (1) F_OFD_GETLK, (2) F_OFD_SETLK, or (3) F_OFD_SETLKW command in an fcntl64 system call.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2015-8966 represents a critical privilege escalation flaw within the Linux kernel's compatibility layer for older ARM architectures. This issue resides in the arch/arm/kernel/sys_oabi-compat.c file and affects kernel versions prior to 4.4, specifically targeting systems that support the old ARM Linux ABI (oabi) for backward compatibility. The vulnerability manifests through improper handling of file locking operations when executed via the fcntl64 system call with specific commands.
The technical flaw stems from insufficient validation of file locking commands within the compatibility layer that translates oabi system calls to the newer native kernel interfaces. When local users execute crafted fcntl64 system calls with F_OFD_GETLK, F_OFD_SETLK, or F_OFD_SETLKW commands, the kernel fails to properly validate the parameters and permissions associated with these operations. This oversight allows malicious processes to manipulate file locking structures in ways that bypass normal access controls and privilege boundaries. The vulnerability specifically exploits the transition between the older oabi and newer native ARM kernel interfaces where the compatibility layer does not adequately enforce the same security checks that would normally be applied to native system calls.
The operational impact of this vulnerability is severe as it enables local attackers to escalate their privileges from regular user level to root access without requiring any special privileges or external exploitation vectors. An attacker with access to a system running an affected kernel version can leverage this flaw to execute arbitrary code with elevated privileges, potentially leading to complete system compromise. The vulnerability affects systems that maintain compatibility with older ARM Linux applications and is particularly concerning in environments where legacy software must continue running alongside modern security practices. Attackers can exploit this through carefully crafted file locking operations that manipulate kernel memory structures, potentially allowing them to modify critical system files or escalate their privileges to gain administrative control over the affected systems.
Mitigation strategies for CVE-2015-8966 primarily involve upgrading to kernel versions 4.4 or later where the vulnerability has been addressed through proper parameter validation and enhanced security checks in the compatibility layer. System administrators should prioritize kernel updates as a critical security measure, particularly in environments where legacy ARM applications are still in use. Additional defensive measures include implementing strict access controls and monitoring for unusual file locking operations, though these are secondary to the primary remediation of kernel upgrades. The vulnerability aligns with CWE-191, which describes integer underflow conditions, and can be mapped to ATT&CK techniques involving privilege escalation through kernel exploits. Organizations should also consider disabling unnecessary compatibility layers and maintaining up-to-date security patches to prevent exploitation of similar vulnerabilities in the kernel's system call handling mechanisms.