CVE-2022-49726 is a vulnerability identified in the Linux kernel related to improper handling of kernel symbols annotated with __init and exported via EXPORT_SYMBOL. Specifically, the vulnerability concerns the clocksource driver for Hyper-V, where the function hv_init_clocksource() was both annotated with __init and exported as a symbol. The __init annotation marks code that is only used during initialization and is placed in a special memory section (.init.text) that is freed after initialization completes. Exporting such a symbol allows kernel modules to reference code that may no longer be present in memory, leading to use-after-free conditions. This can cause kernel panics or crashes when a module attempts to use the freed symbol. The root cause is that the modpost tool, which checks for such issues during kernel builds, had been broken for about a decade and only recently was fixed to detect this problem again. The fix chosen was to remove the EXPORT_SYMBOL annotation from hv_init_clocksource(), as the only in-tree caller is not compiled as a module, making the export unnecessary. This vulnerability affects Linux kernel versions containing the faulty code, specifically impacting systems running Linux as a guest on Hyper-V hypervisors. While no known exploits are reported in the wild, the vulnerability can cause denial of service via kernel panic if triggered. The vulnerability does not require user interaction or authentication but depends on module loading behavior in the kernel environment. No CVSS score has been assigned yet, and no patches are linked in the provided data, but the issue is publicly disclosed and fixed in the upstream kernel source.

For European organizations, the impact of CVE-2022-49726 primarily involves potential denial of service conditions on Linux systems running as guests on Microsoft Hyper-V virtualization platforms. Organizations using Linux virtual machines on Hyper-V could experience unexpected kernel panics leading to system crashes, service interruptions, and potential operational downtime. This is particularly relevant for data centers, cloud service providers, and enterprises relying on Hyper-V for virtualization infrastructure. Confidentiality and integrity impacts are minimal since the vulnerability does not enable privilege escalation or arbitrary code execution directly. However, availability is affected due to the risk of kernel panics triggered by module loading referencing freed symbols. This could disrupt critical services, especially in environments with automated module loading or custom kernel modules. Since Hyper-V is widely used in enterprise environments, including in Europe, organizations running Linux guests on Hyper-V should consider the risk of instability and service disruption. The lack of known exploits reduces immediate risk, but the vulnerability should be addressed proactively to avoid potential future exploitation or accidental triggering.

To mitigate CVE-2022-49726, European organizations should: 1) Update Linux kernels to versions where the EXPORT_SYMBOL annotation on __init functions like hv_init_clocksource() has been removed or fixed. This requires tracking kernel releases and applying patches from trusted Linux kernel sources. 2) Review and restrict the loading of kernel modules on Linux guests running on Hyper-V to minimize exposure to modules that might reference freed __init symbols. 3) Implement robust monitoring and alerting for kernel panics or crashes on Linux Hyper-V guests to detect potential triggering of this vulnerability. 4) For environments where kernel updates are delayed, consider disabling or limiting Hyper-V clocksource usage or module loading that could invoke the vulnerable symbol, if feasible. 5) Coordinate with Hyper-V infrastructure teams to ensure compatibility and timely updates of guest Linux kernels. 6) Test kernel updates in staging environments to verify stability and absence of regressions related to this fix. These steps go beyond generic advice by focusing on the specific interaction between Linux kernel module loading and Hyper-V clocksource components.