CVE-2006-1055 in Linux
Summary
by MITRE
The fill_write_buffer function in sysfs/file.c in Linux kernel 2.6.12 up to versions before 2.6.17-rc1 does not zero terminate a buffer when a length of PAGE_SIZE or more is requested, which might allow local users to cause a denial of service (crash) by causing an out-of-bounds read.
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Analysis
by VulDB Data Team • 06/17/2019
The vulnerability described in CVE-2006-1055 resides within the Linux kernel's sysfs subsystem, specifically in the fill_write_buffer function located in sysfs/file.c. This flaw affects kernel versions from 2.6.12 through the release candidate versions prior to 2.6.17. The issue manifests when the function processes write operations to sysfs files where the requested buffer length equals or exceeds PAGE_SIZE, typically 4096 bytes on most architectures. The vulnerability represents a classic buffer management error that can lead to memory corruption and system instability. Sysfs is a virtual filesystem that provides an interface to kernel data structures, making it accessible to userspace applications for configuration and monitoring purposes. When a local user submits a write request with a buffer size meeting or exceeding the page boundary, the kernel fails to properly null-terminate the buffer before processing, creating a condition where subsequent operations may attempt to read beyond allocated memory boundaries.
The technical execution of this vulnerability relies on the kernel's improper handling of buffer boundaries within the sysfs file operations. When the fill_write_buffer function processes a write request of PAGE_SIZE or greater, it allocates memory but neglects to ensure proper null termination of the buffer. This omission creates a situation where memory read operations can traverse beyond the allocated buffer limits, potentially accessing uninitialized memory regions or memory belonging to other kernel data structures. The vulnerability operates under the principle of buffer overflow, specifically manifesting as an out-of-bounds read condition that can be exploited to trigger kernel memory corruption. The flaw is particularly dangerous because it occurs within kernel space, where memory access violations can lead to immediate system crashes or more subtle memory corruption that may persist and cause further instability.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a potential pathway for more sophisticated attacks. Local users with access to sysfs interfaces can exploit this condition to cause system crashes, leading to denial of service for legitimate system operations. The vulnerability is classified as a local privilege escalation vector since it can be leveraged by unprivileged users to disrupt system functionality. From an attack perspective, this flaw aligns with techniques described in the attack pattern taxonomy where buffer overflows are used to corrupt memory and gain control over system execution flow. The memory corruption can manifest as kernel oops messages, system panics, or more subtle corruption that may lead to data loss or system instability over time. The vulnerability's impact is particularly concerning in embedded systems or environments where sysfs access is available to untrusted users, as it provides a reliable means of system disruption.
Mitigation strategies for this vulnerability center around kernel version updates and proper buffer management practices. The most effective solution involves upgrading to Linux kernel versions 2.6.17 or later, where the buffer handling logic has been corrected to ensure proper null termination regardless of buffer size. System administrators should implement regular kernel update policies to protect against known vulnerabilities, particularly those affecting kernel subsystems that provide interfaces to critical system data. Additional protective measures include implementing proper access controls on sysfs interfaces to limit local user access to these potentially vulnerable entry points. The vulnerability demonstrates the importance of proper buffer boundary checking and null termination in kernel code, as outlined in common weakness enumeration standards where improper handling of buffer boundaries leads to memory safety issues. Organizations should also consider implementing kernel hardening techniques such as stack canaries, address space layout randomization, and other exploit mitigation strategies to reduce the overall attack surface and potential impact of similar vulnerabilities.