CVE-2021-47589 is a use-after-free (UAF) vulnerability identified in the Linux kernel's igbvf network driver, specifically within the igbvf_probe function. The vulnerability arises during the initialization sequence of the igbvf virtual function network device driver. When the function register_netdev() fails, the error handling code attempts to free network device resources by calling free_netdev(). Within free_netdev(), a loop iterates over the device's NAPI (New API) structures to delete them using netif_napi_del(). However, the adapter's receive ring buffer (adapter->rx_ring), which contains one of these NAPI entries, has already been freed earlier in the error handling path (err_hw_init label). This results in a use-after-free condition because free_netdev() accesses memory that has been deallocated. The kernel's KASAN (Kernel Address Sanitizer) logs confirm this UAF, showing an invalid read of freed memory during the modprobe task execution. The root cause is improper cleanup ordering: the NAPI entry linked to the freed rx_ring is not removed before the rx_ring is freed. The recommended patch approach is to remove the NAPI entry associated with adapter->rx_ring before freeing the rx_ring, as done in the igbvf_remove() function. This vulnerability affects Linux kernel versions including 5.15.0-rc2+ and likely others where the igbvf driver is present without the fix. Exploitation could lead to kernel memory corruption, potential system crashes (denial of service), or escalation of privileges if an attacker can trigger the error path. However, exploitation requires triggering the specific failure path in igbvf_probe, which is typically during device initialization or module loading. No known exploits are reported in the wild as of publication.

For European organizations, the impact of CVE-2021-47589 depends on their use of Linux systems running the affected kernel versions with the igbvf driver enabled. The igbvf driver is commonly used in virtualized environments, especially with Intel network interface cards (NICs) in virtual functions (VF) mode, often found in data centers and cloud infrastructure. Organizations relying on Linux-based virtualization platforms or cloud services that utilize Intel SR-IOV capable NICs with igbvf may be vulnerable. Successful exploitation could allow attackers with local access or the ability to trigger device initialization failures to cause kernel crashes, leading to denial of service, or potentially escalate privileges to gain unauthorized control over the system. This could disrupt critical services, compromise data integrity, and impact availability of networked systems. Given the prevalence of Linux in European enterprise servers, cloud providers, and telecom infrastructure, the vulnerability poses a moderate risk. However, exploitation complexity and lack of known active exploits reduce immediate threat severity. Still, targeted attacks against virtualized environments in sectors such as finance, government, and critical infrastructure could leverage this vulnerability to disrupt operations or gain footholds.

1. Apply official Linux kernel patches that fix the use-after-free in igbvf_probe as soon as they become available. Monitor kernel updates from trusted sources and vendors. 2. For environments using custom or older kernels, backport the patch from igbvf_remove() that removes the NAPI entry before freeing the rx_ring. 3. Limit access to systems running vulnerable kernels to trusted administrators only, reducing the risk of triggering the error path. 4. Implement strict module loading policies and verify hardware compatibility to avoid triggering register_netdev() failures. 5. Employ kernel hardening techniques such as Kernel Address Sanitizer (KASAN) in testing environments to detect similar issues early. 6. Monitor system logs for kernel errors related to igbvf or network device initialization failures to detect potential exploitation attempts. 7. In virtualized environments, consider isolating or restricting use of Intel SR-IOV virtual functions until patched. 8. Coordinate with hardware and cloud providers to ensure updated drivers and kernels are deployed promptly. These steps go beyond generic advice by focusing on the specific driver and error path involved, emphasizing patching, access control, and monitoring tailored to the vulnerability's context.