CVE-2026-18917 in Red Hat
Summary
by MITRE • 08/20/2026
A flaw was found in libvirt. An unprivileged local user could exploit an integer overflow vulnerability in the NodeGetFreePages RPC handler. This flaw allows crafted values to bypass a size check, leading to an undersized memory buffer. Subsequently, real NUMA node data can overwrite this buffer. This heap buffer overflow can corrupt the root libvirt daemon's memory, potentially leading to a denial of service or local privilege escalation.
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Analysis
by VulDB Data Team • 08/20/2026
The vulnerability identified in libvirt represents a critical security flaw within the NodeGetFreePages Remote Procedure Call handler, specifically affecting systems utilizing Non-Uniform Memory Access architectures. This issue stems from an integer overflow condition that occurs during the processing of user-supplied input parameters. When an unprivileged local user interacts with this specific RPC endpoint, they can supply crafted numerical values designed to exploit weaknesses in the arithmetic operations used for buffer size calculations. The core technical failure lies in the application's inability to correctly validate these inputs against expected bounds before allocating memory resources. By manipulating the integer values passed during the request, an attacker can cause the calculated buffer size to wrap around or result in a significantly smaller allocation than intended by the system logic. This miscalculation leads directly to the creation of an undersized heap buffer that is insufficient to hold the actual data payload being processed.
Once this inadequate memory region is allocated, the subsequent operation involves copying real NUMA node free page statistics into the designated buffer. Because the allocated space is smaller than the incoming data stream due to the initial integer overflow error, a classic heap buffer overflow occurs. The excess data spills over the boundaries of the allocated block, corrupting adjacent memory structures on the heap. In the context of libvirt, which operates as a privileged daemon managing virtualization resources, such corruption can have severe consequences for the integrity and stability of the host system. The overwritten memory may contain critical control data or pointers used by the root-level libvirtd process, thereby compromising its operational state. This type of memory corruption is particularly dangerous because it does not require high privileges to initiate; any local user account on the compromised machine can trigger the exploit vector through standard API calls exposed by the daemon.
The operational impact of this vulnerability is twofold, encompassing both availability and confidentiality concerns depending on how the corrupted memory is interpreted by the executing process. The most immediate consequence is a denial of service condition where the libvirt daemon crashes or becomes unresponsive due to fatal memory errors triggered by the heap corruption. This disrupts virtual machine management capabilities for all users relying on that instance of the daemon, effectively halting administrative operations and potentially causing downtime for running workloads managed through libvirt. However, the more severe risk involves local privilege escalation. If an attacker can carefully craft the overflow payload to overwrite specific function pointers or return addresses within the daemon's memory space, they may achieve arbitrary code execution with the privileges of the root user running the libvirtd process. This would allow complete control over the host system, enabling further attacks such as data exfiltration, persistence mechanisms, or lateral movement across connected virtual networks.
From a classification perspective, this vulnerability aligns closely with CWE-190 Integer Overflow and CWE-122 Heap-based Buffer Overflow within the Common Weakness Enumeration framework. The exploitation technique maps to MITRE ATT&CK techniques related to privilege escalation via memory corruption, specifically leveraging improper input validation to bypass security checks that are intended to prevent buffer overruns. Defense in depth strategies must be employed to mitigate this risk since client-side protections alone may not suffice if the daemon itself lacks robust boundary checking. Immediate mitigation involves applying vendor-provided patches that address the integer arithmetic logic within the NodeGetFreePages handler and ensure proper bounds verification before memory allocation occurs. Administrators should also consider restricting access to libvirt RPC endpoints where possible, utilizing network segmentation or firewall rules to limit exposure of management interfaces to trusted networks only. Additionally enabling strict sandboxing for virtual machines can reduce the blast radius if a guest OS is compromised and attempts to interact with host-level services through vulnerable daemons like libvirt. Regular auditing of system logs for abnormal daemon restarts or memory errors can also serve as an early detection mechanism for attempted exploitation activities targeting this specific flaw.