CVE-2021-47464 in Linux
Summary
by MITRE • 05/22/2024
In the Linux kernel, the following vulnerability has been resolved:
audit: fix possible null-pointer dereference in audit_filter_rules
Fix possible null-pointer dereference in audit_filter_rules.
audit_filter_rules() error: we previously assumed 'ctx' could be null
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Analysis
by VulDB Data Team • 05/14/2025
The vulnerability identified as CVE-2021-47464 represents a critical null-pointer dereference issue within the Linux kernel's audit subsystem. This flaw exists in the audit_filter_rules() function which is responsible for processing audit rules and filtering system calls based on configured policies. The vulnerability stems from an assumption made during code development that the context parameter 'ctx' would always contain a valid reference, when in reality this pointer could legitimately be null under certain error conditions or specific operational scenarios.
The technical implementation of this vulnerability occurs within the audit subsystem's rule filtering mechanism where the kernel attempts to process audit rules without proper validation of the context pointer. When the audit_filter_rules() function executes and encounters a null context pointer, it proceeds to dereference this invalid memory location, leading to an immediate system crash or potential privilege escalation. This type of error falls under the CWE-476 category of Null Pointer Dereference, which is classified as a fundamental programming error that can result in system instability or security compromise. The vulnerability manifests as a kernel oops or system panic when the audit subsystem processes certain malformed or edge-case audit rules.
The operational impact of CVE-2021-47464 extends beyond simple system crashes to potentially enable privilege escalation attacks within the kernel space. An attacker who can trigger the specific conditions that lead to this null pointer dereference may be able to cause the kernel to crash or potentially manipulate the execution flow to gain elevated privileges. The audit subsystem is typically enabled in production environments for security monitoring and compliance purposes, making this vulnerability particularly concerning as it affects systems that rely on audit logging for security controls. According to ATT&CK framework category T1059.003, this vulnerability could be exploited to achieve code execution in kernel space, representing a significant threat to system integrity and security posture.
Mitigation strategies for CVE-2021-47464 require immediate patch application from the Linux kernel maintainers, as the fix involves adding proper null pointer validation before dereferencing the context parameter in the audit_filter_rules() function. System administrators should prioritize updating their kernel versions to include the patched code that properly validates the ctx parameter before attempting to access its members. Additionally, monitoring for audit subsystem errors and system crashes related to audit rule processing should be implemented as part of security operations. The fix aligns with standard security practices for preventing null pointer dereferences and represents a defensive programming approach that validates all pointer parameters before use. Organizations should also review their audit rule configurations to ensure that malformed or potentially problematic rules are not being introduced into the system, as this vulnerability may be triggered by specific combinations of audit rule parameters that create the null context condition.