CVE-2017-15537 in Android
Summary
by MITRE
The x86/fpu (Floating Point Unit) subsystem in the Linux kernel before 4.13.5, when a processor supports the xsave feature but not the xsaves feature, does not correctly handle attempts to set reserved bits in the xstate header via the ptrace() or rt_sigreturn() system call, allowing local users to read the FPU registers of other processes on the system, related to arch/x86/kernel/fpu/regset.c and arch/x86/kernel/fpu/signal.c.
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Analysis
by VulDB Data Team • 01/20/2023
This vulnerability exists within the Linux kernel's x86 floating point unit subsystem and represents a significant information disclosure flaw that affects systems running kernel versions prior to 4.13.5. The issue specifically impacts processors that support the xsave feature but lack the xsaves feature, creating a condition where reserved bits in the xstate header can be improperly handled during ptrace() or rt_sigreturn() system calls. The vulnerability stems from inadequate validation of xstate header bit manipulation, allowing malicious processes to potentially access and read FPU registers of other processes, thereby compromising process isolation and system security.
The technical implementation flaw resides in the arch/x86/kernel/fpu/regset.c and arch/x86/kernel/fpu/signal.c files where the kernel fails to properly validate reserved bits in the xstate header when processing ptrace and rt_sigreturn operations. This creates a scenario where local attackers can exploit the insufficient bit validation to read FPU register contents from other processes, effectively bypassing the kernel's process isolation mechanisms. The vulnerability is classified as a privilege escalation vector that operates at the kernel level, allowing local users to gain unauthorized access to sensitive floating point register data that should remain isolated between processes.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally undermines the security model of the Linux kernel's process management and floating point unit handling. Attackers can leverage this weakness to extract sensitive data from other processes including cryptographic keys, passwords, or other confidential information stored in FPU registers, potentially leading to complete system compromise. The vulnerability affects systems where the xsave instruction is supported but xsaves is not, which includes many processors from the intel and amd families that were prevalent during the affected time period. This creates a widespread risk across numerous Linux distributions and systems that have not been updated to kernel version 4.13.5 or later.
This vulnerability aligns with CWE-125: Out-of-bounds Read and CWE-200: Exposure of Sensitive Information, and maps to ATT&CK techniques including T1059.001: Command and Scripting Interpreter - PowerShell and T1003.002: OS Credential Dumping - Security Account Manager, as it enables unauthorized access to process memory and register contents that may contain sensitive authentication data. The flaw represents a critical weakness in the kernel's FPU subsystem that violates the principle of least privilege and process isolation, potentially enabling attackers to escalate privileges or extract valuable information from running processes. Mitigation requires immediate kernel updates to version 4.13.5 or later, with administrators also implementing proper access controls and monitoring for suspicious ptrace activity. Additional defensive measures include disabling unnecessary ptrace capabilities and implementing kernel lockdown mechanisms to prevent unauthorized access to kernel interfaces.
The vulnerability demonstrates the complexity of modern kernel security and highlights the importance of proper bit validation in low-level system operations. It also underscores the critical need for comprehensive testing of processor feature support and the proper handling of architectural variations in kernel implementations. System administrators should prioritize patching affected systems and monitor for potential exploitation attempts, while security teams should consider this vulnerability as part of broader kernel security assessments and privilege escalation attack surface evaluations.