CVE-2021-47276 is a vulnerability identified in the Linux kernel specifically affecting the ftrace subsystem on the arm64 architecture. The issue arises from improper handling of instruction pointer (ip) addresses within the ftrace_bug() function. When a bug in ftrace_init() attempts to update instructions to no-operations (nop), an error path returns -EINVAL instead of -EFAULT. This causes ftrace_bug() to blindly read the ip address without verifying its validity. If the ip address points to an invalid memory location, this results in a kernel panic due to an unsafe memory access. The vulnerability is rooted in the kernel's failure to safely access the ip address, which can lead to system crashes. The fix involves using copy_from_kernel_nofault() to safely read the ip address, which prevents faults by handling invalid memory access gracefully and reporting faults instead of causing a panic. This vulnerability is specific to arm64 Linux kernel versions identified by the commit hash 05736a427f7e16be948ccbf39782bd3a6ae16b14 and was published on May 21, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations running Linux on arm64 architectures, this vulnerability could lead to unexpected system crashes (kernel panics) when the ftrace subsystem encounters this specific error condition. This impacts system availability, potentially causing downtime for critical services relying on affected Linux kernels. While the vulnerability does not appear to allow privilege escalation or code execution, the denial of service caused by kernel panics can disrupt operations, especially in environments where arm64 Linux servers are used for cloud infrastructure, edge computing, or embedded systems. Organizations with high availability requirements or those operating critical infrastructure could face operational interruptions. Since no known exploits exist, the immediate risk is moderate, but unpatched systems remain vulnerable to accidental or targeted triggering of this bug, which could be leveraged in denial-of-service attacks.

European organizations should prioritize updating their Linux kernels to versions that include the patch for CVE-2021-47276. Specifically, kernel versions incorporating the fix that replaces direct ip address reads with copy_from_kernel_nofault() should be deployed. For environments where immediate patching is not feasible, organizations should monitor kernel logs for ftrace-related errors and consider disabling ftrace functionality if it is not essential, as a temporary mitigation. Additionally, implementing robust system monitoring and automated reboot mechanisms can help reduce downtime caused by unexpected panics. Organizations should also ensure that their incident response and business continuity plans account for potential kernel panics in arm64 Linux systems. Finally, maintaining strict control over kernel module loading and limiting access to kernel debugging features can reduce the risk of exploitation.