Incorrect mapping of Executable bits in Fuchsia Kernel

The core of this vulnerability lies in the incorrect handling of UXN (User eXecute Not-Allowed) and PXN (Privileged eXecute Not-Allowed) bits within the mmuflagstos1pte_attr function. Specifically, the vulnerability allows an attacker to map privileged executable pages as executable from an unprivileged context, effectively bypassing kernel-mode executability restrictions from user-mode. Conversely, it also permits mapping unprivileged executable pages as executable from a privileged context, circumventing user-mode restrictions from kernel-mode. This dual bypass significantly expands the attack surface. Successful exploitation could lead to arbitrary code execution within the kernel, granting the attacker complete control over the Fuchsia system. The ability to execute arbitrary code in kernel mode represents a severe compromise, potentially allowing for data theft, system modification, and denial of service.

Systems running Fuchsia OS, particularly those with limited security controls or exposed to untrusted user input, are at risk. Devices utilizing Fuchsia for embedded systems or IoT applications should be prioritized for patching. Development environments and testing systems running Fuchsia are also vulnerable.

• linux / server: Monitor kernel logs for unusual memory mapping activity or attempts to execute code from unprivileged contexts. Use journalctl -k to filter for relevant kernel messages.

journalctl -k | grep -i 'mmu_flags_to_s1_pte_attr'

• linux / server: Employ auditd rules to track modifications to memory protection settings.

auditctl -w /path/to/kernel/module -p x -k kernel_mmu

• generic web: While not directly applicable to web applications, monitor system-level processes for unexpected kernel module loading or execution.

1. 2022-01-18Disclosure

   disclosure

1. आरक्षित2021-01-05
2. प्रकाशित2022-01-18
3. संशोधित2024-08-03
4. EPSS अद्यतन2026-04-02

The primary mitigation for CVE-2021-22566 is to upgrade the Fuchsia Kernel to version 7d731b4e9599088ac3073956933559da7bca6a00 or later. Due to the nature of the vulnerability and its impact on kernel-level memory protection, there are no readily available workarounds beyond upgrading. Consider implementing stricter access controls and privilege separation within the Fuchsia environment to limit the potential impact of a successful exploit. Regularly review and audit kernel configurations to ensure adherence to security best practices. After upgrading, verify the fix by attempting to execute a user-mode process with elevated privileges and confirming that the attempt is denied.