CVE-2026-23268 in Linux
Summary
by MITRE • 03/18/2026
In the Linux kernel, the following vulnerability has been resolved:
apparmor: fix unprivileged local user can do privileged policy management
An unprivileged local user can load, replace, and remove profiles by opening the apparmorfs interfaces, via a confused deputy attack, by passing the opened fd to a privileged process, and getting the privileged process to write to the interface.
This does require a privileged target that can be manipulated to do the write for the unprivileged process, but once such access is achieved full policy management is possible and all the possible implications that implies: removing confinement, DoS of system or target applications by denying all execution, by-passing the unprivileged user namespace restriction, to exploiting kernel bugs for a local privilege escalation.
The policy management interface can not have its permissions simply changed from 0666 to 0600 because non-root processes need to be able to load policy to different policy namespaces.
Instead ensure the task writing the interface has privileges that are a subset of the task that opened the interface. This is already done via policy for confined processes, but unconfined can delegate access to the opened fd, by-passing the usual policy check.
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Analysis
by VulDB Data Team • 06/01/2026
The vulnerability described in CVE-2026-23268 represents a critical privilege escalation flaw within the Linux kernel's AppArmor security module. This issue stems from a confused deputy attack pattern where an unprivileged local user can manipulate privileged processes to perform administrative policy operations on their behalf. The flaw specifically affects the apparmorfs interface mechanisms that control policy management operations, creating a pathway for unauthorized users to bypass normal security boundaries and execute privileged actions. The vulnerability operates through a sophisticated delegation attack vector where the unprivileged user opens the policy management interface and then passes the file descriptor to a privileged process, which subsequently performs the requested operations on behalf of the attacker.
The technical implementation of this vulnerability exploits the fundamental design assumption that file descriptor passing between processes maintains proper access controls and privilege boundaries. When an unprivileged user opens the apparmorfs interface, they create a file descriptor that can be passed to privileged processes through legitimate system calls. However, the kernel's privilege validation mechanism fails to properly verify that the process performing the write operation has equivalent or appropriate privileges to those that originally opened the interface. This allows the unprivileged user to effectively delegate their access rights to privileged processes, effectively circumventing the intended security model that separates unprivileged user operations from privileged policy management functions. The vulnerability specifically targets the kernel's handling of file descriptor passing and privilege validation in the context of AppArmor's policy management interfaces.
The operational impact of this vulnerability extends far beyond simple privilege escalation, encompassing a broad spectrum of potential security violations and system compromise scenarios. An attacker who successfully exploits this vulnerability can perform complete policy management operations including loading new profiles, replacing existing ones, and removing security constraints from the system. This capability enables sophisticated attack vectors such as removing confinement from critical system processes, causing denial of service by blocking application execution, bypassing user namespace restrictions, and potentially exploiting other kernel vulnerabilities to achieve full system compromise. The implications are particularly severe because AppArmor's policy management interfaces are designed to be accessible to non-root users for namespace-specific operations, but the vulnerability allows these same interfaces to be manipulated for system-wide administrative purposes. This vulnerability directly violates the principle of least privilege and can be leveraged to establish persistent access or escalate privileges to root level.
The remediation approach for this vulnerability requires implementing stricter privilege validation mechanisms that ensure the process performing operations on the apparmorfs interface maintains privileges that are a subset of those that originally opened the interface. This solution addresses the root cause by preventing the delegation of access rights from unprivileged to privileged contexts, thereby maintaining the intended security boundaries within the AppArmor framework. The fix must balance the legitimate need for non-root processes to load policies into different namespaces while preventing the specific attack pattern that allows privilege escalation. This approach aligns with the principle of privilege separation and follows established security patterns for preventing confused deputy attacks. The solution also incorporates defensive programming practices that validate access rights at each stage of the file descriptor handling process, ensuring that the privilege model remains intact even when file descriptors are passed between processes. This vulnerability demonstrates the critical importance of proper privilege validation in kernel interfaces and aligns with CWE-284 (Improper Access Control) and ATT&CK technique T1068 (Exploitation for Privilege Escalation) in the MITRE ATT&CK framework.