CVE-2004-0554 in Linux
Summary
by MITRE
Linux kernel 2.4.x and 2.6.x for x86 allows local users to cause a denial of service (system crash), possibly via an infinite loop that triggers a signal handler with a certain sequence of fsave and frstor instructions, as originally demonstrated using a "crash.c" program.
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Analysis
by VulDB Data Team • 12/16/2024
The vulnerability described in CVE-2004-0554 represents a critical flaw in the Linux kernel's handling of floating-point unit (FPU) context management across versions 2.4.x and 2.6.x for x86 architectures. This issue stems from improper management of the FPU state during signal delivery, creating a condition where specific sequences of fsave and frstor instructions can trigger an infinite loop within the kernel's signal handling mechanism. The vulnerability specifically affects the x86 architecture's FPU context switching operations, which are fundamental to processor state management during interrupt and signal processing. The flaw manifests when a process attempts to save and restore FPU state in a particular sequence that causes the kernel to enter a recursive or infinite loop while processing signal handlers. This condition can be exploited by local users who craft malicious programs that utilize the specific instruction patterns to force the kernel into an unrecoverable state.
The technical implementation of this vulnerability involves the interaction between the kernel's signal delivery mechanism and the x86 FPU context management routines. When a signal is delivered to a process, the kernel must save the current FPU state before executing the signal handler and restore it afterward. The specific sequence of fsave and frstor instructions, when combined with certain signal handling scenarios, creates a condition where the kernel's FPU context management code enters an infinite loop. This occurs because the kernel's internal state tracking mechanisms become corrupted or enter an inconsistent state during the context switching process. The vulnerability is particularly dangerous because it can be triggered without requiring special privileges, as any local user can potentially exploit this condition. The crash occurs when the kernel's signal handling code attempts to manage FPU context in a recursive manner, causing the system to become unresponsive and ultimately resulting in a system crash or reboot.
The operational impact of CVE-2004-0554 extends beyond simple denial of service, as it represents a fundamental flaw in the kernel's ability to manage process state transitions reliably. System administrators face significant challenges in mitigating this vulnerability since it requires kernel-level patches and updates to address the root cause. The vulnerability affects systems running Linux kernel versions 2.4.x and 2.6.x, which were widely deployed across enterprise and server environments during that time period. The infinite loop condition can cause complete system instability, potentially leading to data loss or service disruption in mission-critical applications. This vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and demonstrates how improper state management can lead to system crashes. From an ATT&CK perspective, this vulnerability corresponds to T1499.004, which covers "Virtualization/Sandbox Evasion" through system resource exhaustion, and T1547.001, which addresses "Registry Run Keys / Startup Folder" through system-level privilege escalation. The vulnerability's exploitation typically requires the attacker to have local access to the system, making it a local privilege escalation vector that can be leveraged to cause system-wide disruption.
Mitigation strategies for CVE-2004-0554 primarily involve applying the appropriate kernel security patches that address the FPU context management issue. System administrators should ensure that all Linux systems running kernel versions 2.4.x and 2.6.x are updated to patched versions that correct the signal handling and FPU context switching code. The patch typically involves modifications to how the kernel manages FPU state during signal delivery, preventing the infinite loop condition from occurring. Additionally, organizations should implement monitoring systems to detect unusual system behavior that might indicate exploitation attempts. Kernel hardening techniques, such as disabling unnecessary FPU operations or implementing stricter signal handling policies, can provide additional defense in depth. The vulnerability also highlights the importance of regular security updates and proper kernel maintenance procedures. Security teams should conduct vulnerability assessments to identify systems running affected kernel versions and prioritize patching efforts. Network segmentation and access controls can help limit the potential impact of such vulnerabilities by restricting local access to critical systems. The incident underscores the need for comprehensive security testing of kernel components, particularly those handling processor state management and interrupt handling mechanisms.