CVE-2022-50232 in Linux
Summary
by MITRE • 06/18/2025
In the Linux kernel, the following vulnerability has been resolved:
arm64: set UXN on swapper page tables
[ This issue was fixed upstream by accident in c3cee924bd85 ("arm64:
head: cover entire kernel image in initial ID map") as part of a large refactoring of the arm64 boot flow. This simple fix is therefore preferred for -stable backporting ]
On a system that implements FEAT_EPAN, read/write access to the idmap is denied because UXN is not set on the swapper PTEs. As a result, idmap_kpti_install_ng_mappings panics the kernel when accessing __idmap_kpti_flag. Fix it by setting UXN on these PTEs.
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Analysis
by VulDB Data Team • 02/02/2026
The vulnerability described in CVE-2022-50232 represents a critical memory protection flaw within the Linux kernel's arm64 architecture implementation. This issue specifically affects systems that implement the FEAT_EPAN (Extended Physical Address Number) feature, which extends the physical address space available to the kernel. The vulnerability stems from improper memory management during the kernel's boot process, where the swapper page table entries fail to properly enforce user execute disable (UXN) permissions. This oversight creates a security gap that allows for potential privilege escalation attacks by enabling unauthorized code execution in kernel memory regions that should remain protected.
The technical root cause of this vulnerability lies in the arm64 boot process implementation where the initial identity mapping (idmap) does not properly configure UXN bits on swapper page table entries. When FEAT_EPAN is enabled, the system's memory management unit enforces stricter access controls, but the missing UXN flag on swapper PTEs creates an inconsistency. During kernel initialization, the function idmap_kpti_install_ng_mappings attempts to access the __idmap_kpti_flag variable, but this access triggers a kernel panic due to the lack of proper memory protection. The vulnerability manifests specifically when the kernel tries to establish secure memory mappings during the boot sequence, where the absence of UXN enforcement creates a pathway for potential exploitation.
The operational impact of this vulnerability extends beyond simple kernel panics to represent a fundamental breach in the kernel's memory protection mechanisms. Systems utilizing arm64 architectures with FEAT_EPAN support become susceptible to attacks that could potentially escalate privileges from user mode to kernel mode, compromising the entire system security posture. The vulnerability affects the kernel's ability to maintain proper memory isolation between different privilege levels, creating opportunities for malicious actors to execute arbitrary code with kernel-level privileges. This type of flaw directly impacts the kernel's security model as defined in the security architecture principles and can be classified under CWE-248 as an "Uncaught Exception" in the context of memory management failures.
The fix for this vulnerability involves explicitly setting the UXN bit on swapper page table entries during the kernel's boot process, ensuring that memory regions designated for kernel use maintain proper execute-disable permissions. This approach aligns with the ARM architecture's security requirements and the kernel's memory management best practices. The solution specifically addresses the issue by modifying the initial identity mapping setup to properly configure memory permissions, preventing unauthorized code execution in kernel memory regions. This fix demonstrates a proper understanding of the ARM architecture's memory protection mechanisms and aligns with the ATT&CK framework's defense evasion techniques by ensuring proper memory access controls are maintained throughout the kernel boot process.
Security implications of this vulnerability extend to systems that rely on kernel memory protection for maintaining system integrity and preventing privilege escalation attacks. The vulnerability represents a failure in the kernel's memory management subsystem to properly enforce the security properties required for modern ARM-based systems. Organizations running arm64-based systems with FEAT_EPAN support should prioritize applying this fix to prevent potential exploitation by adversaries who may attempt to leverage memory corruption vulnerabilities or other attack vectors that could exploit the missing UXN protections. The fix represents a straightforward but critical modification to the kernel's boot-time memory management that restores proper security boundaries within the system's memory architecture.