CVE-2018-16882 in Linux
Summary
by MITRE • 01/25/2023
A use-after-free issue was found in the way the Linux kernel's KVM hypervisor processed posted interrupts when nested(=1) virtualization is enabled. In nested_get_vmcs12_pages(), in case of an error while processing posted interrupt address, it unmaps the 'pi_desc_page' without resetting 'pi_desc' descriptor address, which is later used in pi_test_and_clear_on(). A guest user/process could use this flaw to crash the host kernel resulting in DoS or potentially gain privileged access to a system. Kernel versions before 4.14.91 and before 4.19.13 are vulnerable.
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Analysis
by VulDB Data Team • 06/23/2023
The vulnerability described in CVE-2018-16882 represents a critical use-after-free flaw within the Linux kernel's KVM hypervisor implementation, specifically affecting systems utilizing nested virtualization. This issue manifests in the posted interrupt handling mechanism when the nested virtualization feature is enabled with the nested parameter set to one. The vulnerability resides in the kernel's virtualization subsystem where the KVM hypervisor manages virtual machine interrupts and their processing between host and guest environments. The flaw occurs during the processing of posted interrupts, which are essential for efficient interrupt handling in virtualized environments where multiple virtual machines share the same physical hardware resources.
The technical implementation of this vulnerability stems from improper memory management within the nested_get_vmcs12_pages() function, which is responsible for managing virtual machine control structures in nested virtualization scenarios. When an error condition occurs during the processing of the posted interrupt address, the kernel code incorrectly unmaps the pi_desc_page memory region while failing to reset the associated pi_desc descriptor address variable. This creates a situation where a freed memory reference persists in the system, leading to undefined behavior when the pi_test_and_clear_on() function later attempts to access this stale descriptor. The underlying issue aligns with CWE-416, which specifically addresses use-after-free vulnerabilities where memory is accessed after it has been freed, and represents a classic example of improper resource management in kernel space code.
The operational impact of this vulnerability extends beyond simple denial of service, presenting significant security implications for virtualized environments. A malicious guest user or process within a virtual machine can exploit this flaw to trigger a kernel crash on the host system, effectively causing a denial of service condition that disrupts all virtual machines running on that host. More critically, the vulnerability could potentially be leveraged to achieve privilege escalation, allowing guest users to gain elevated privileges on the host system and potentially compromise the entire virtualization infrastructure. This represents a serious threat to cloud computing environments, containerized deployments, and any system relying on KVM-based virtualization where guest isolation is paramount for security. The vulnerability affects systems running kernel versions prior to 4.14.91 and 4.19.13, making it particularly concerning for organizations maintaining older kernel versions in production environments.
Mitigation strategies for CVE-2018-16882 primarily focus on kernel updates and system hardening measures. Organizations should immediately apply the security patches released by the Linux kernel community, updating to kernel versions 4.14.91 or later, or 4.19.13 and newer, which contain the necessary fixes for this use-after-free condition. The patch addresses the memory management issue by ensuring proper cleanup of the pi_desc descriptor address when errors occur during posted interrupt processing, preventing the use-after-free scenario. System administrators should also consider disabling nested virtualization where it is not strictly required, as this eliminates the attack surface for this specific vulnerability. Additional monitoring should be implemented to detect potential exploitation attempts, particularly in environments where guest users have elevated privileges or where multiple virtual machines are running on shared hosts. The vulnerability demonstrates the importance of proper memory management in kernel space code and highlights the need for comprehensive testing of virtualization features, particularly those involving complex interrupt handling mechanisms that are critical for system stability and security in virtualized environments. This vulnerability also relates to ATT&CK technique T1055.011, which involves the exploitation of kernel vulnerabilities for privilege escalation, and underscores the critical nature of maintaining up-to-date kernel security patches in enterprise virtualization deployments.