CVE-2026-72458 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
apparmor: fix NULL pointer dereference in unpack_pdb
pdb->dfa could be NULL if unpack_dfa fails, causing a NULL pointer dereference.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides within the Linux kernel's AppArmor security module where a critical NULL pointer dereference flaw exists in the unpack_pdb function. This issue occurs when the unpack_dfa function fails to properly initialize the dfa member of the pdb structure, leaving pdb->dfa as a null pointer. The AppArmor subsystem relies on proper initialization of these data structures to enforce mandatory access controls and security policies within the kernel space. When unpack_dfa encounters an error condition during the parsing or construction of deterministic finite automata used for policy evaluation, it returns without setting up the dfa member correctly, creating a dangerous state where subsequent code attempts to dereference this null pointer.
The technical exploitation of this vulnerability demonstrates a classic null pointer dereference pattern that can lead to kernel crashes and system instability. The unpack_pdb function processes policy data blocks that contain security policies for AppArmor modules, and when the dfa initialization fails, the code path continues without proper error handling. This flaw directly violates the principle of defensive programming where all pointers should be validated before dereferencing, as outlined in the CWE-476 standard for null pointer dereference vulnerabilities. The vulnerability affects the kernel's memory management and security enforcement mechanisms, potentially allowing an attacker to trigger a denial of service condition by crafting malicious policy data that causes unpack_dfa to fail.
The operational impact of this vulnerability extends beyond simple system crashes as it represents a potential attack vector for privilege escalation or system compromise. When the kernel encounters a NULL pointer dereference in kernel space, the immediate consequence is a kernel oops or panic that terminates the affected process and may cause broader system instability. In environments where AppArmor policies are actively enforced, an attacker could potentially exploit this condition to disrupt security services or gain unauthorized access to system resources. The vulnerability aligns with ATT&CK technique T1068 which involves exploiting privileges to escalate access within a system, as the compromised kernel module could undermine the security boundaries that AppArmor is designed to maintain.
Mitigation strategies for this vulnerability involve ensuring proper error handling and validation of pointer initialization before use. Kernel developers should implement comprehensive checks to verify that unpack_dfa successfully initializes all members of the pdb structure before proceeding with operations that might dereference these pointers. The fix typically requires adding null pointer validation immediately after unpack_dfa returns, ensuring that if the function fails, the calling code either handles the error gracefully or prevents further execution paths that would attempt to access the uninitialized dfa member. System administrators should ensure kernel updates are applied promptly to address this vulnerability, as it represents a fundamental security flaw in the kernel's AppArmor implementation that could be exploited by malicious actors with local access to manipulate policy data.