CVE-2023-1838 in Linux
Summary
by MITRE • 04/05/2023
A use-after-free flaw was found in vhost_net_set_backend in drivers/vhost/net.c in virtio network subcomponent in the Linux kernel due to a double fget. This flaw could allow a local attacker to crash the system, and could even lead to a kernel information leak problem.
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Analysis
by VulDB Data Team • 10/17/2025
The vulnerability identified as CVE-2023-1838 represents a critical use-after-free flaw within the Linux kernel's vhost_net subsystem, specifically in the vhost_net_set_backend function located in drivers/vhost/net.c. This flaw stems from a double fget implementation that creates a race condition in the kernel's virtualization framework, affecting the virtio network subcomponent that facilitates network communication between virtual machines and host systems. The vulnerability manifests when the kernel fails to properly manage file descriptor references during vhost network backend configuration, creating a scenario where freed memory can be accessed after deallocation.
The technical exploitation of this vulnerability occurs through a local attacker who can manipulate the vhost_net subsystem to trigger the double fget condition, resulting in memory management corruption that leads to system crashes. The flaw operates at the kernel level where the vhost_net_set_backend function handles the assignment of network backend devices for virtualized network interfaces, making it a core component in virtual machine networking operations. When the double fget occurs, it creates a situation where the same file descriptor reference can be freed and subsequently accessed, leading to undefined behavior that can result in kernel memory corruption and system instability.
From an operational perspective, this vulnerability poses significant risks to systems running virtualized environments where vhost_net is enabled, as it can be exploited by local attackers with minimal privileges to cause denial of service conditions or potentially escalate to information disclosure scenarios. The impact extends beyond simple system crashes to include potential kernel memory leaks that could expose sensitive information about kernel memory layout or internal structures. This vulnerability affects various Linux distributions that implement virtualization features using the vhost_net subsystem, particularly those running kernel versions that include the affected code path. The flaw's exploitation requires local access to the system and the ability to interact with the vhost_net interface, making it more limited in scope compared to remote exploits but still highly concerning in multi-tenant or containerized environments.
Security mitigations for CVE-2023-1838 should focus on immediate kernel updates that address the double fget implementation in the vhost_net subsystem, ensuring proper reference counting and synchronization mechanisms are in place. System administrators should disable vhost_net functionality when not required for virtualized environments, and implement monitoring for unusual system behavior that might indicate exploitation attempts. The vulnerability aligns with CWE-416, which addresses use-after-free conditions in memory management, and can be mapped to ATT&CK technique T1059 for privilege escalation scenarios where local attackers might leverage kernel vulnerabilities. Organizations should also consider implementing kernel hardening measures such as stack canaries and kernel address space layout randomization to increase the difficulty of exploitation. The fix typically involves correcting the reference counting logic in the vhost_net_set_backend function to prevent the double fget scenario that leads to the use-after-free condition, ensuring that file descriptor references are properly managed throughout the network backend assignment process.