CVE-2002-1319 in Linux
Summary
by MITRE
The Linux kernel 2.4.20 and earlier, and 2.5.x, when running on x86 systems, allows local users to cause a denial of service (hang) via the emulation mode, which does not properly clear TF and NT EFLAGs.
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Analysis
by VulDB Data Team • 08/13/2025
The vulnerability identified as CVE-2002-1319 represents a critical flaw in the Linux kernel's handling of processor flags during emulation mode on x86 architectures. This issue affects kernel versions 2.4.20 and earlier, as well as the 2.5.x development series, making it a long-standing security concern that persisted across multiple kernel releases. The flaw specifically manifests in how the kernel manages the Trap Flag (TF) and Nested Task (NT) bits within the EFLAGS register during the execution of emulated instructions.
The technical implementation of this vulnerability stems from improper flag clearing mechanisms within the kernel's emulation subsystem. When the kernel executes instructions in emulation mode, particularly those involving system call emulation or other privileged operations, it fails to properly clear the TF and NT bits in the EFLAGS register. The Trap Flag (TF) is used to enable single-stepping of instructions for debugging purposes, while the Nested Task flag (NT) indicates whether a task is nested within another task. When these flags remain set during emulation operations, they can cause unexpected behavior in the processor's execution flow.
The operational impact of this vulnerability is significant as it allows local attackers to induce a system hang or denial of service condition. Since the vulnerability exists within the kernel's core execution pathways, an attacker with local access can exploit this weakness to cause the system to become unresponsive. The hang occurs because the improperly set flags can interfere with normal processor operation, particularly when the kernel attempts to handle interrupts or perform context switches. This type of vulnerability directly impacts system availability and can be leveraged to disrupt critical services running on affected systems.
This vulnerability aligns with CWE-122 which addresses improper restriction of operations within a recognized security boundary, and relates to the broader category of kernel-level privilege escalation and denial of service attacks. From an ATT&CK framework perspective, this flaw maps to techniques involving privilege escalation and denial of service, specifically targeting the kernel's execution environment. The vulnerability demonstrates how seemingly minor flag management issues can cascade into significant system stability problems. The exploitation requires local system access but does not require special privileges beyond what is normally available to a user, making it particularly concerning for multi-user systems where local access might be obtained through various attack vectors.
Mitigation strategies for CVE-2002-1319 primarily involve upgrading to kernel versions that have addressed this specific flag clearing issue. System administrators should immediately patch affected systems with kernel versions that properly clear the TF and NT flags during emulation operations. Additionally, monitoring systems for unusual hang patterns or process behavior that might indicate exploitation attempts can serve as an early warning mechanism. The fix typically involves modifications to the kernel's emulation code to ensure proper flag management during instruction execution, specifically ensuring that the EFLAGS register is correctly manipulated when entering and exiting emulation contexts. Organizations should also implement proper access controls and privilege management to limit local user access where possible, reducing the attack surface for this type of vulnerability.