Source: cve@mitre.org
The linux 2.4 kernel before 2.4.19 assumes that the fninit instruction clears all registers, which could lead to an information leak on processors that do not clear all relevant SSE registers.
Critical vulnerability in Linux kernel versions prior to 2.4.19 allows for information leakage due to an incorrect assumption about the fninit instruction. This flaw can expose sensitive data stored in SSE registers, potentially leading to unauthorized access and system compromise.
Step 1: Triggering the Vulnerability: A malicious process, or a process controlled by an attacker, executes code that leverages the SSE registers. This code stores sensitive data (e.g., cryptographic keys, passwords, or other confidential information) within these registers.
Step 2: Context Switching: The operating system performs a context switch, potentially switching to a different process.
Step 3: Kernel Initialization: The kernel, due to the vulnerability, assumes that fninit has cleared all SSE registers during the context switch. However, on affected systems, this is not guaranteed.
Step 4: Data Leakage: The new process, or a process controlled by the attacker, can then read the contents of the SSE registers. Because the registers were not fully cleared, they may contain sensitive data from the previous process.
Step 5: Information Disclosure: The attacker gains access to the sensitive data, leading to information disclosure and potential system compromise.
The vulnerability stems from an incorrect assumption within the Linux kernel's initialization routines. Specifically, the kernel's code, prior to version 2.4.19, assumed that the fninit instruction, used to initialize the floating-point unit (FPU) and SSE registers, would clear all relevant registers. However, on some processors, particularly those with SSE support, fninit might not fully clear all SSE registers. This leads to a scenario where sensitive data, previously stored in these registers by other processes or the kernel itself, could be inadvertently leaked to a malicious actor. The root cause is a logic error in the kernel's initialization sequence, where the code relies on an incomplete initialization of the SSE registers. This is not a buffer overflow or a race condition, but rather a data leakage vulnerability due to an incorrect assumption about hardware behavior.
This vulnerability is unlikely to be actively targeted by sophisticated APTs today, given its age. However, it could be incorporated into a larger exploit chain, especially if targeting legacy systems. CISA KEV status: Not Listed.
Monitor system logs for unusual process behavior, especially processes that frequently perform context switches and utilize SSE instructions.
Analyze memory dumps for residual data in SSE registers after context switches.
Implement host-based intrusion detection systems (HIDS) to identify suspicious memory access patterns.
Network traffic analysis to identify data exfiltration attempts after a context switch.
Upgrade the Linux kernel to version 2.4.19 or later. This is the primary and most effective remediation.
If upgrading is not immediately possible, consider disabling SSE instructions if they are not required by the system's applications. This is a drastic measure and may impact performance.
Implement memory sanitization techniques to ensure that sensitive data is cleared from registers before context switches, though this is difficult to implement retroactively.
Regularly audit system configurations and ensure that all security patches are applied promptly.