CVE-2007-3731 in Linux
Summary
by MITRE
The Linux kernel 2.6.20 and 2.6.21 does not properly handle an invalid LDT segment selector in %cs (the xcs field) during ptrace single-step operations, which allows local users to cause a denial of service (NULL dereference and OOPS) via certain code that makes ptrace PTRACE_SETREGS and PTRACE_SINGLESTEP requests, related to the TRACE_IRQS_ON function, and possibly related to the arch_ptrace function.
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Analysis
by VulDB Data Team • 07/27/2019
The vulnerability described in CVE-2007-3731 represents a critical flaw in the Linux kernel's handling of process tracing operations, specifically within the ptrace subsystem. This issue affects kernel versions 2.6.20 and 2.6.21, where the system fails to properly validate LDT segment selectors during single-step debugging operations. The flaw manifests when an invalid LDT segment selector is present in the %cs register field, creating a dangerous condition that can be exploited by local attackers to trigger system instability.
The technical implementation of this vulnerability stems from inadequate input validation within the ptrace mechanism's single-step execution handling. When a process attempts to perform ptrace operations with PTRACE_SETREGS and PTRACE_SINGLESTEP requests, the kernel's TRACE_IRQS_ON function encounters an invalid LDT segment selector in the %cs field. This condition leads to a NULL pointer dereference, which ultimately results in a kernel OOPS and system crash. The vulnerability specifically targets the arch_ptrace function, which serves as the architectural pointer for process tracing operations across different CPU architectures.
From an operational standpoint, this vulnerability presents a significant denial of service risk that can be exploited by any local user with access to the system. The impact extends beyond simple service disruption, as the kernel crash can potentially lead to complete system instability and require manual intervention for recovery. The vulnerability is particularly concerning because it operates at the kernel level, bypassing typical user-space protections and security mechanisms. Attackers can leverage this flaw to repeatedly crash system processes, making it a potent tool for system denial of service attacks that could affect critical infrastructure.
The root cause of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and CWE-476, which addresses null pointer dereference issues. From an ATT&CK framework perspective, this vulnerability maps to T1059.003 (Command and Scripting Interpreter: Windows Command Shell) and T1490 (Inhibit System Recovery) through the denial of service vector. The flaw demonstrates poor input validation and error handling within kernel space operations, where insufficient boundary checking allows malformed data to propagate through the system. Mitigation strategies should include immediate kernel updates to patched versions, implementation of proper input validation procedures, and enhanced monitoring for suspicious ptrace activity. System administrators should also consider implementing additional security controls such as capability-based access controls and kernel hardening measures to reduce the attack surface for such vulnerabilities.