CVE-2011-4081 in Linux
Summary
by MITRE
crypto/ghash-generic.c in the Linux kernel before 3.1 allows local users to cause a denial of service (NULL pointer dereference and OOPS) or possibly have unspecified other impact by triggering a failed or missing ghash_setkey function call, followed by a (1) ghash_update function call or (2) ghash_final function call, as demonstrated by a write operation on an AF_ALG socket.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability described in CVE-2011-4081 represents a critical NULL pointer dereference issue within the Linux kernel's cryptographic subsystem, specifically in the ghash implementation located in crypto/ghash-generic.c. This flaw affects Linux kernel versions prior to 3.1 and demonstrates how improper error handling in cryptographic operations can lead to system instability and potential security implications. The vulnerability manifests when the ghash_setkey function fails or is missing, creating a state where subsequent cryptographic operations cannot properly execute due to uninitialized or invalid pointers.
The technical exploitation of this vulnerability occurs through manipulation of AF_ALG socket operations, which are part of the Linux kernel's algorithm interface framework designed to provide userspace access to cryptographic algorithms. When an attacker performs a write operation on an AF_ALG socket, they can trigger a sequence where the ghash_setkey function fails or is not properly executed, leaving the cryptographic context in an inconsistent state. Subsequently, calling either the ghash_update or ghash_final functions on this malformed context results in a NULL pointer dereference, causing the kernel to crash with an OOPS message and potentially leading to a complete system denial of service.
This vulnerability impacts the fundamental security model of Linux systems by creating a path for local users to destabilize kernel operations without requiring elevated privileges. The flaw aligns with CWE-476 which identifies NULL pointer dereference as a common weakness in software development, particularly in kernel space where such errors can have catastrophic consequences. The operational impact extends beyond simple denial of service as the vulnerability could potentially allow for more sophisticated attacks if attackers can leverage the kernel crash to execute arbitrary code or manipulate system state. The issue particularly affects systems that rely on cryptographic operations for network security, data protection, and authentication services.
The mitigation strategy for CVE-2011-4081 requires immediate kernel updates to version 3.1 or later where the vulnerability has been addressed through proper error handling and validation of cryptographic context states. System administrators should prioritize patching affected systems and monitor for potential exploitation attempts through AF_ALG socket operations. Additionally, implementing proper input validation and error handling in cryptographic subsystems can help prevent similar issues in other components. The vulnerability demonstrates the importance of robust error handling in kernel space operations, particularly when dealing with cryptographic algorithms where improper state management can lead to system instability. Organizations should also consider implementing monitoring solutions that can detect unusual AF_ALG socket activity patterns that might indicate exploitation attempts. This issue highlights the need for comprehensive testing of cryptographic implementations and proper validation of all function call sequences in kernel modules to prevent similar NULL pointer dereference vulnerabilities from compromising system security and availability.