CVE-2000-0157 in NetBSD
Summary
by MITRE
NetBSD ptrace call on VAX allows local users to gain privileges by modifying the PSL contents in the debugging process.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-2000-0157 represents a critical privilege escalation flaw within the NetBSD operating system's ptrace implementation on VAX architecture systems. This issue stems from insufficient validation of process state registers during debugging operations, specifically targeting the Program Status Long (PSL) register contents that control processor execution mode and privilege levels. The flaw exists in the kernel-level ptrace system call handling mechanism, which is designed to allow one process to observe and control the execution of another process for debugging purposes.
The technical exploitation of this vulnerability occurs when a local user with access to a debugging process can manipulate the PSL register contents through ptrace calls. The PSL register contains crucial bits that determine whether the processor is operating in user mode or kernel mode, along with interrupt enable flags and other execution control parameters. By modifying these register values, an attacker can potentially transition the debugging process from user mode to kernel mode, effectively gaining root privileges on the system. This represents a classic case of privilege escalation through register manipulation in kernel debugging interfaces.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as it fundamentally undermines the security model of the NetBSD system. Attackers can leverage this flaw to execute arbitrary code with the highest system privileges, potentially leading to complete system compromise. The vulnerability affects all NetBSD systems running on VAX architecture that have ptrace functionality enabled, making it particularly concerning given the widespread use of VAX systems in enterprise environments during the early 2000s. The attack vector is particularly dangerous because it requires only local access to the system, eliminating the need for network connectivity or complex remote exploitation techniques.
This vulnerability aligns with CWE-264, which classifies issues related to permissions, privileges, and access controls, specifically addressing the improper handling of process state during debugging operations. The flaw also maps to ATT&CK technique T1068, which covers 'Local Privilege Escalation' through the exploitation of system-level vulnerabilities. The root cause analysis reveals that the ptrace implementation failed to properly validate register modifications against the current privilege context, allowing users to manipulate critical execution state information that should remain protected from user-space modification. Security professionals should note that this vulnerability demonstrates the importance of maintaining strict privilege boundaries even within kernel debugging interfaces and highlights the necessity of comprehensive input validation in system call implementations. The fix typically involves implementing proper register validation checks within the ptrace system call handler to prevent unauthorized modification of privilege-critical register contents, ensuring that only legitimate debugging operations can modify processor state information that affects execution privileges.