CVE-2016-9313 in Linux
Summary
by MITRE
security/keys/big_key.c in the Linux kernel before 4.8.7 mishandles unsuccessful crypto registration in conjunction with successful key-type registration, which allows local users to cause a denial of service (NULL pointer dereference and panic) or possibly have unspecified other impact via a crafted application that uses the big_key data type.
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Analysis
by VulDB Data Team • 10/04/2022
The vulnerability described in CVE-2016-9313 represents a critical flaw in the Linux kernel's key management subsystem, specifically within the big_key.c file that handles the registration and management of big key types. This issue affects Linux kernel versions prior to 4.8.7 and demonstrates a fundamental problem in how the kernel processes cryptographic registration failures in conjunction with successful key-type registrations. The flaw occurs when the kernel attempts to register a cryptographic algorithm but fails, while simultaneously successfully registering a key type that depends on that cryptographic algorithm. This mismanagement creates a dangerous state where subsequent operations can trigger a NULL pointer dereference, leading to system crashes and potential denial of service conditions.
The technical implementation of this vulnerability stems from improper error handling within the kernel's key management framework. When a cryptographic registration fails, the system should properly clean up resources and prevent further operations that could lead to system instability. However, in the affected kernel versions, the failure to properly handle this specific error condition allows a local attacker to craft malicious applications that exploit the race condition between key-type registration and cryptographic algorithm registration. The flaw specifically manifests when an application attempts to use the big_key data type, which requires both a key type and underlying cryptographic support. When the cryptographic registration fails but the key type registration succeeds, the kernel maintains a partially initialized state that becomes exploitable.
The operational impact of CVE-2016-9313 extends beyond simple denial of service scenarios, as the vulnerability can potentially lead to more severe consequences depending on the execution environment and system configuration. Local users with minimal privileges can leverage this flaw to cause system panics and kernel oops, effectively rendering the affected system unstable and unusable. The vulnerability's classification under CWE-476 indicates it involves a NULL pointer dereference, which is a common and dangerous pattern in kernel space programming that can lead to privilege escalation or information disclosure in more complex exploitation scenarios. The attack vector requires local access to the system, making it particularly concerning for environments where untrusted users might have shell access or where privilege separation is inadequate.
Mitigation strategies for CVE-2016-9313 primarily involve upgrading to Linux kernel version 4.8.7 or later, which contains the necessary patches to properly handle the cryptographic registration failure scenario. System administrators should prioritize kernel updates, particularly in production environments where the vulnerability could be exploited to cause service disruption. Additional protective measures include implementing proper privilege controls to limit local user access, monitoring for unusual kernel panic patterns, and maintaining comprehensive system logging to detect potential exploitation attempts. The vulnerability also highlights the importance of robust error handling in kernel space code and demonstrates how seemingly minor registration order issues can lead to catastrophic system failures. Organizations should consider implementing security monitoring solutions that can detect kernel-level anomalies and ensure that all systems are regularly updated with the latest security patches to prevent exploitation of known vulnerabilities. This particular flaw serves as a reminder of the critical importance of proper resource management and error handling in operating system kernels, where improper state management can lead to complete system compromise.