CVE-2004-0565 in Linux
Summary
by MITRE
Floating point information leak in the context switch code for Linux 2.4.x only checks the MFH bit but does not verify the FPH owner, which allows local users to read register values of other processes by setting the MFH bit.
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Analysis
by VulDB Data Team • 06/28/2019
This vulnerability exists in the Linux kernel version 2.4.x family and represents a critical information disclosure flaw in the floating point unit context switching mechanism. The vulnerability stems from an incomplete implementation of the floating point state management during process switches, specifically failing to properly validate the ownership of floating point registers before allowing access to them. The issue occurs when the kernel checks only the MFH (Math Fault Handler) bit in the floating point control register without verifying that the current process actually owns the floating point state, creating a window where malicious processes can access another process's floating point register contents.
The technical exploitation of this vulnerability relies on the kernel's improper validation logic during context switches, where the MFH bit is set to indicate that floating point registers have been modified but the system fails to confirm that the process currently accessing these registers is the legitimate owner. This design flaw allows local attackers to manipulate the MFH bit and subsequently read floating point register values from other processes, effectively bypassing the kernel's floating point state protection mechanisms. The vulnerability is particularly dangerous because it operates at the kernel level and can be exploited by unprivileged local users who have access to the system, making it a significant concern for system security and process isolation.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially expose sensitive data contained in floating point registers, including cryptographic keys, passwords, or other confidential information that may be processed using floating point operations. Attackers could leverage this information leak to perform more sophisticated attacks, such as privilege escalation or targeted data extraction from other running processes. The vulnerability affects all Linux 2.4.x kernel versions and represents a fundamental flaw in the kernel's floating point state management, which is critical for maintaining proper process isolation and security boundaries within the operating system.
This vulnerability maps directly to CWE-200, which covers "Information Exposure," and specifically relates to improper access control mechanisms in kernel-level floating point state management. The issue also aligns with ATT&CK technique T1059.003, which involves the use of local commands and scripts to exploit system vulnerabilities, as attackers would need to craft specific code to manipulate the MFH bit and access other processes' floating point state. Additionally, this vulnerability demonstrates poor privilege separation and inadequate validation of kernel-level access controls, making it a prime example of how incomplete security checks in system-level code can create serious information leakage risks. The recommended mitigation involves upgrading to Linux kernel versions 2.6.x or later, where proper floating point state management has been implemented, along with ensuring that all floating point register access is properly validated against process ownership to prevent unauthorized access to sensitive floating point state information.