CVE-2006-1855 in Linux
Summary
by MITRE
choose_new_parent in Linux kernel before 2.6.11.12 includes certain debugging code, which allows local users to cause a denial of service (panic) by causing certain circumstances involving termination of a parent process.
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Analysis
by VulDB Data Team • 06/19/2019
The vulnerability identified as CVE-2006-1855 resides within the Linux kernel's process management subsystem, specifically in the choose_new_parent function that governs how child processes are reassigned when their parent process terminates. This flaw represents a classic case of debugging code remaining in production code, where developers inadvertently left diagnostic functionality intact during the kernel's development cycle. The issue affects Linux kernel versions prior to 2.6.11.12, indicating that this was a relatively early vulnerability in the kernel's lifecycle that persisted due to oversight during the release process. The vulnerability's classification aligns with CWE-457: Use of Uninitialized Variables, as the debugging code references uninitialized memory locations that can trigger system instability when specific process termination scenarios occur.
The technical exploitation of this vulnerability occurs when a process hierarchy undergoes specific termination patterns that trigger the debugging code path within choose_new_parent. This debugging code, designed to assist kernel developers in understanding parent-child process relationships, contains logic that can cause the kernel to attempt operations on invalid memory references or process structures. When a local user can orchestrate the precise sequence of process creation and termination that activates this code path, the kernel's response becomes unpredictable and ultimately leads to system panic. The vulnerability's nature suggests that it operates at the kernel level where memory management and process scheduling are handled, making it particularly dangerous as it can compromise the entire system's stability without requiring elevated privileges beyond local access.
From an operational impact perspective, this vulnerability represents a significant denial of service risk for systems running affected kernel versions. Local users can reliably trigger system panics that result in complete system crashes and require manual rebooting to restore functionality. The attack vector is relatively straightforward since it only requires local access and knowledge of process management patterns that can trigger the specific debugging code path. The vulnerability's impact extends beyond simple service disruption as kernel panics can potentially lead to data loss if systems are not properly safeguarded against unexpected shutdowns, particularly in mission-critical environments where system uptime is paramount. Organizations running vulnerable kernel versions face the risk of repeated service interruptions and potential data integrity issues during the exploitation window.
Mitigation strategies for CVE-2006-1855 focus primarily on kernel version updates, as the vulnerability was resolved through the inclusion of proper code removal in kernel 2.6.11.12. System administrators should prioritize immediate patching of all affected systems to eliminate the risk of exploitation. Additionally, implementing monitoring solutions that can detect unusual process termination patterns may help identify potential exploitation attempts. The vulnerability's remediation aligns with the principle of least privilege where local users should not be able to cause system-wide panics through normal system operations. Security teams should also consider implementing kernel hardening measures and ensuring that debugging code is properly disabled in production environments. This vulnerability serves as a reminder of the critical importance of thorough code review processes and the need for comprehensive testing of kernel code before release, particularly in production environments where such oversight can lead to severe operational consequences. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service tactics, emphasizing the need for comprehensive system hardening and regular security updates to maintain system integrity and availability.