CVE-2011-2496 in Linux
Summary
by MITRE
Integer overflow in the vma_to_resize function in mm/mremap.c in the Linux kernel before 2.6.39 allows local users to cause a denial of service (BUG_ON and system crash) via a crafted mremap system call that expands a memory mapping.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/03/2021
The vulnerability described in CVE-2011-2496 represents a critical integer overflow condition within the Linux kernel's memory management subsystem that specifically affects the vma_to_resize function in the mm/mremap.c file. This flaw exists in kernel versions prior to 2.6.39 and demonstrates a classic security issue where improper input validation leads to system instability. The vulnerability is categorized under CWE-190 as an integer overflow or wraparound, which occurs when an integer value exceeds its maximum representable range and wraps around to a smaller value, creating unexpected behavior in the system's memory management operations.
The technical implementation of this vulnerability involves the mremap system call, which is used to change the size of an existing memory mapping. When a local user crafts a specific mremap request that attempts to expand a memory mapping beyond certain boundaries, the vma_to_resize function fails to properly validate the integer parameters involved in the memory expansion calculation. This failure results in an integer overflow that causes the kernel to trigger a BUG_ON macro, leading to an immediate system crash and complete denial of service for the affected system. The vulnerability specifically exploits the lack of proper bounds checking in the memory management code path that handles memory mapping resizing operations.
From an operational perspective, this vulnerability poses significant risk to Linux systems as it allows any local user to execute a denial of service attack against the kernel itself. The impact extends beyond simple service disruption since kernel crashes can lead to complete system instability and require manual rebooting of affected machines. This vulnerability particularly affects systems running kernel versions before 2.6.39, making it a critical concern for organizations maintaining legacy systems or those that have not yet applied the necessary security patches. The attack vector requires local access but does not require special privileges, making it accessible to any user account on the system and potentially exploitable by malicious insiders or compromised accounts.
The mitigation strategies for this vulnerability primarily involve upgrading to kernel version 2.6.39 or later, where the integer overflow has been properly addressed through enhanced input validation and bounds checking. System administrators should also implement monitoring solutions to detect unusual mremap system call patterns that might indicate exploitation attempts. Additionally, organizations should maintain comprehensive patch management procedures to ensure timely deployment of kernel security updates. The vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, though in this case the attack is local rather than network-based, demonstrating how local privilege escalation techniques can be leveraged to cause system-wide denial of service conditions. The fix implemented in the patched kernel versions includes proper integer overflow detection and handling within the memory management subsystem, preventing the malicious mremap operations from triggering the BUG_ON condition that leads to system crashes.