CVE-2006-7203 in Linux
Summary
by MITRE
The compat_sys_mount function in fs/compat.c in Linux kernel 2.6.20 and earlier allows local users to cause a denial of service (NULL pointer dereference and oops) by mounting a smbfs file system in compatibility mode ("mount -t smbfs").
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Analysis
by VulDB Data Team • 07/20/2019
The vulnerability described in CVE-2006-7203 represents a critical denial of service flaw within the Linux kernel's compatibility layer for version 2.6.20 and earlier. This issue specifically targets the compat_sys_mount function located in the fs/compat.c file, which handles mounting operations when the system operates in compatibility mode. The vulnerability arises when a local user attempts to mount an smbfs filesystem using the command "mount -t smbfs", triggering a NULL pointer dereference that results in a kernel oops and subsequent system crash.
The technical flaw stems from inadequate input validation within the compatibility mount handling code. When the smbfs filesystem type is specified in compatibility mode, the function fails to properly initialize or validate required data structures before attempting to dereference pointers. This NULL pointer dereference occurs because the code assumes certain kernel structures will be properly allocated and initialized, but in this specific scenario involving smbfs compatibility mounting, these assumptions prove incorrect. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with the ability to execute mount commands, regardless of their privilege level.
The operational impact of this vulnerability extends beyond simple system downtime, as it can be leveraged to create persistent denial of service conditions that may require manual intervention to resolve. Local attackers can repeatedly trigger this condition to keep systems unstable, making it particularly problematic in multi-user environments where system administrators cannot rely on consistent service availability. The kernel oops generated by this vulnerability typically results in system crashes that require rebooting, potentially causing data loss and service interruptions. This type of vulnerability is categorized under CWE-476 as NULL pointer dereference, which represents a fundamental memory management flaw that can lead to system instability.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, as it can be used to disrupt system availability even when the attack vector originates from within the local system. The exploit requires minimal privileges and can be automated, making it particularly dangerous in environments where local access is not properly restricted. The vulnerability demonstrates how compatibility layers in operating systems can introduce unexpected security risks, as the code path for handling older system calls may not have been thoroughly tested for all possible input combinations. System administrators should note that this vulnerability affects systems running Linux kernel versions up to and including 2.6.20, making it crucial to implement timely kernel updates and patches to prevent exploitation. The flaw also highlights the importance of proper kernel testing procedures, particularly for compatibility modes that handle legacy filesystem types, as these code paths often receive less rigorous security scrutiny than core system functions.