CVE-2022-49520 is a vulnerability in the Linux kernel specifically affecting the arm64 architecture's compatibility syscall handling. The issue arises when a 32-bit compat process attempts to execute an unknown or invalid system call number above the defined __ARM_NR_COMPAT_END threshold. Instead of properly handling this invalid syscall, the kernel incorrectly treats the syscall number as an exception syndrome register (ESR_ELx) value. This leads to misleading error messages being printed to the kernel log (dmesg), suggesting erroneous exception causes such as pointer authentication faults, which are unrelated to the actual invalid syscall. The root cause is that the kernel sets the fault_code field to the invalid syscall number rather than zero or a valid ESR_ELx value. This causes arm64_show_signal() to interpret and display bogus exception information. The vulnerability does not allow privilege escalation or direct exploitation but results in confusing diagnostic output that can mislead system administrators and developers during debugging or incident response. The fix involves modifying compat_arm_syscall() to set the ESR_ELx value to zero when an invalid syscall is detected, preventing the printing of incorrect exception syndrome information. This change improves the accuracy and clarity of kernel logs when invalid syscalls occur. The vulnerability affects Linux kernel versions prior to the fix and is specific to arm64 architectures running 32-bit compatibility mode processes. There are no known exploits in the wild, and the issue primarily impacts diagnostic clarity rather than system security or stability directly.

For European organizations, the direct security impact of CVE-2022-49520 is low since it does not enable privilege escalation, code execution, or denial of service. However, the misleading kernel log messages can complicate incident response and troubleshooting efforts on affected arm64 Linux systems. Organizations relying on arm64 servers or embedded devices running 32-bit compatibility mode may experience confusion when diagnosing system faults or security incidents, potentially delaying remediation. This could be particularly relevant for sectors with critical infrastructure or industrial control systems using arm64 Linux platforms. Misinterpretation of kernel logs could lead to misallocated resources or overlooked real issues. The impact is more operational and diagnostic rather than a direct threat to confidentiality, integrity, or availability. Nonetheless, maintaining accurate and trustworthy system logs is important for compliance and security monitoring in European regulatory environments such as GDPR and NIS Directive.

1. Apply the official Linux kernel patches that address CVE-2022-49520 as soon as they become available for your distribution or kernel version. 2. For organizations using custom or embedded arm64 Linux kernels, backport the fix to your kernel branch to ensure accurate syscall error reporting. 3. Educate system administrators and security teams about this issue to prevent misinterpretation of kernel logs related to invalid syscalls on arm64 compat processes. 4. Use additional diagnostic tools such as strace to accurately identify invalid syscalls rather than relying solely on kernel log messages. 5. Monitor kernel logs for suspicious or unexpected syscall activity and correlate with other security telemetry to avoid false positives caused by this vulnerability. 6. Where possible, minimize the use of 32-bit compatibility mode on arm64 systems to reduce exposure to this and similar issues. 7. Maintain up-to-date documentation and incident response playbooks that reflect this vulnerability's nature to improve troubleshooting efficiency.