CVE-2011-2928 in Linux
Summary
by MITRE
The befs_follow_link function in fs/befs/linuxvfs.c in the Linux kernel before 3.1-rc3 does not validate the length attribute of long symlinks, which allows local users to cause a denial of service (incorrect pointer dereference and OOPS) by accessing a long symlink on a malformed Be filesystem.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 11/18/2021
The vulnerability identified as CVE-2011-2928 resides within the Linux kernel's BeFS (Be File System) implementation, specifically in the befs_follow_link function located at fs/befs/linuxvfs.c. This flaw represents a classic case of insufficient input validation that can be exploited to cause system instability. The vulnerability affects Linux kernel versions prior to 3.1-rc3, indicating it was present in a significant portion of the kernel's development lifecycle. The core issue stems from the function's failure to properly validate the length attribute of long symbolic links, creating a critical gap in the kernel's security posture.
The technical exploitation of this vulnerability occurs when a local attacker creates or encounters a malformed Be filesystem containing a long symbolic link with an invalid length attribute. When the kernel's befs_follow_link function attempts to process such a symlink, it performs an incorrect pointer dereference operation that leads to an OOPS condition. This kernel panic occurs because the function assumes the length attribute is valid and proceeds with memory operations that result in accessing invalid memory addresses. The flaw essentially allows an attacker to manipulate the kernel's memory management routines through legitimate file system operations, bypassing normal security checks that would typically prevent such invalid memory access patterns.
From an operational impact perspective, this vulnerability presents a significant denial of service risk that can compromise system stability and availability. The OOPS condition generated by the incorrect pointer dereference causes the kernel to crash, potentially resulting in system hangs or reboots that disrupt normal operations. While the vulnerability requires local access to exploit, it can be particularly dangerous in environments where system stability is critical, such as servers or embedded systems where unexpected reboots could lead to service interruption or data loss. The impact extends beyond simple service disruption as kernel panics can potentially lead to data corruption or loss if the system crashes during critical operations.
The vulnerability aligns with CWE-129, which addresses improper validation of length attributes in array access operations, and demonstrates characteristics consistent with ATT&CK technique T1499.004 for network denial of service. The flaw represents a privilege escalation vector within the kernel space, as local users can leverage the vulnerability to cause system-wide instability. Mitigation strategies should focus on updating to kernel versions 3.1-rc3 or later where the validation has been properly implemented. System administrators should also consider implementing additional monitoring for kernel OOPS conditions and ensuring that all systems running BeFS file systems are regularly updated. Additionally, the vulnerability highlights the importance of proper input validation in kernel space operations and serves as a reminder that even seemingly minor flaws in filesystem implementations can have significant security implications when exploited locally.