CVE-2011-4110 in Linux
Summary
by MITRE
The user_update function in security/keys/user_defined.c in the Linux kernel 2.6 allows local users to cause a denial of service (NULL pointer dereference and kernel oops) via vectors related to a user-defined key and "updating a negative key into a fully instantiated key."
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Analysis
by VulDB Data Team • 11/29/2021
The vulnerability described in CVE-2011-4110 represents a critical flaw in the Linux kernel's key management subsystem that enables local attackers to trigger a denial of service condition through a specific race condition involving user-defined keys. This vulnerability exists within the user_update function located in security/keys/user_defined.c of the Linux kernel version 2.6, where improper handling of key state transitions creates an exploitable path for privilege escalation and system instability. The flaw specifically manifests when attempting to update a negative key into a fully instantiated key, creating a scenario where the kernel's internal pointer management fails catastrophically. The underlying technical issue stems from insufficient validation of key states during the update process, allowing an attacker to manipulate the kernel's keyring subsystem into a state where a NULL pointer dereference occurs, resulting in an immediate kernel oops and system crash.
The operational impact of this vulnerability extends beyond simple denial of service as it represents a fundamental breakdown in kernel memory management and state validation mechanisms. When exploited, the vulnerability can cause complete system instability leading to kernel panic and forced reboot of affected systems, effectively rendering the machine unavailable to legitimate users and potentially disrupting critical services. This type of vulnerability is particularly dangerous in multi-user environments or systems where local access is possible, as it allows unprivileged users to compromise system availability. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and demonstrates how improper state management in kernel space can lead to complete system compromise. From an attack perspective, this vulnerability falls under ATT&CK technique T1068 which covers 'Exploitation for Privilege Escalation' and T1499 which addresses 'Endpoint Denial of Service', making it a significant concern for system administrators and security professionals.
Mitigation strategies for CVE-2011-4110 require immediate kernel updates to patched versions that properly validate key states before allowing transitions from negative to instantiated states. System administrators should prioritize applying security patches from their respective kernel vendors and ensure all systems running affected kernel versions are updated promptly. Additionally, implementing monitoring solutions that can detect anomalous kernel behavior or keyring subsystem activity may help identify potential exploitation attempts. The vulnerability highlights the importance of proper input validation and state management in kernel space code, particularly for subsystems handling security-critical data structures. Organizations should also consider implementing least privilege principles and restricting local access to critical systems where possible, as this vulnerability requires local user access to exploit effectively. Regular security audits of kernel subsystems and proactive vulnerability management programs are essential to prevent similar issues from occurring in the future, as this vulnerability demonstrates how seemingly minor state transition issues can lead to complete system compromise and availability denial.