CVE-2006-5701 in Linux
Summary
by MITRE
Double free vulnerability in squashfs module in the Linux kernel 2.6.x, as used in Fedora Core 5 and possibly other distributions, allows local users to cause a denial of service by mounting a crafted squashfs filesystem.
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Analysis
by VulDB Data Team • 04/26/2026
The vulnerability identified as CVE-2006-5701 represents a critical double free error within the squashfs filesystem module of the Linux kernel version 2.6.x series. This flaw exists in the handling of crafted squashfs filesystems and specifically affects Fedora Core 5 distributions along with potentially other Linux variants that utilize the same kernel version. The vulnerability stems from improper memory management practices within the kernel's squashfs implementation where the same memory block gets freed twice during the processing of malformed filesystem structures. This type of vulnerability falls under the CWE-415 category of double free conditions, which is a well-documented memory corruption flaw that can lead to unpredictable system behavior and potential privilege escalation opportunities.
The technical execution of this vulnerability occurs when a local attacker mounts a specially crafted squashfs filesystem that contains malformed data structures. During the filesystem mounting process, the kernel's squashfs module fails to properly validate the integrity of the filesystem metadata, leading to a scenario where memory allocation functions are called multiple times on the same memory segment. This double free condition creates a state where the kernel's memory allocator receives invalid memory pointers, potentially leading to heap corruption that can be exploited to cause system instability. The vulnerability is classified as a local privilege escalation vector since it requires a user to have the ability to mount filesystems, which typically requires either user-level access or specific system permissions.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as the double free error can potentially be leveraged to execute arbitrary code within kernel space. When the kernel's memory management subsystem encounters the corrupted memory state, it may lead to memory allocation failures that can cause the system to crash or become unresponsive. In some exploitation scenarios, attackers might be able to manipulate the heap layout to achieve more sophisticated attacks, including privilege escalation to root level access. The vulnerability affects systems running kernel versions 2.6.x where the squashfs module was compiled with support for the filesystem, making it particularly concerning for server environments and systems where users might have the ability to mount external storage devices or create custom filesystem images.
Mitigation strategies for CVE-2006-5701 primarily focus on immediate patching of affected kernel versions, with the most effective solution being the application of kernel updates that contain memory management fixes for the squashfs module. System administrators should also implement strict filesystem mounting policies that prevent untrusted users from mounting arbitrary filesystems, particularly when dealing with external storage devices or user-supplied content. Network segmentation and privilege separation techniques can help reduce the attack surface by limiting user access to filesystem mounting capabilities. The vulnerability demonstrates the importance of proper input validation and memory management in kernel space, aligning with ATT&CK technique T1068 which covers privilege escalation through kernel exploits. Organizations should also implement monitoring solutions to detect unusual filesystem mounting activities and ensure that all kernel components undergo thorough security testing before deployment in production environments. The remediation process requires careful consideration of system compatibility and testing procedures to ensure that kernel updates do not introduce regressions in existing functionality while effectively addressing the memory corruption vulnerability.