CVE-2024-25940 in FreeBSD
Summary
by MITRE • 02/15/2024
`bhyveload -h ` may be used to grant loader access to the directory tree on the host. Affected versions of bhyveload(8) do not make any attempt to restrict loader's access to , allowing the loader to read any file the host user has access to. In the bhyveload(8) model, the host supplies a userboot.so to boot with, but the loader scripts generally come from the guest image. A maliciously crafted script could be used to exfiltrate sensitive data from the host accessible to the user running bhyhveload(8), which is often the system root.
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Analysis
by VulDB Data Team • 06/05/2025
The vulnerability identified as CVE-2024-25940 affects the bhyveload utility in FreeBSD systems, specifically targeting the host system's directory access controls during virtual machine boot processes. This issue stems from the bhyveload(8) command's failure to properly restrict file system access permissions when loading virtual machine boot components. The flaw occurs because the utility does not implement adequate access controls to prevent the loader from traversing the host file system beyond its intended scope, creating a significant security risk in virtualization environments. The vulnerability is particularly concerning as it allows unauthorized access to sensitive host resources through the loader component that is typically considered a trusted boot mechanism.
The technical implementation of this vulnerability lies in the bhyveload(8) utility's handling of file system paths and access permissions during the virtual machine boot process. When the host system provides a userboot.so file for booting virtual machines, the utility typically relies on guest image scripts for the loader configuration. However, the flaw allows maliciously crafted scripts to exploit the lack of path restriction mechanisms, enabling the loader to read files from the host system that the executing user has access to. This represents a classic privilege escalation vulnerability where the host user's permissions are inadvertently extended to the loader process. The vulnerability is classified under CWE-22 as Improper Limitation of a Pathname to a Restricted Directory, which specifically addresses the issue of insufficient path traversal controls in system components.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides a potential attack vector for data exfiltration from the host system. When the bhyveload(8) utility is executed with root privileges, which is common in production environments, a malicious script could access sensitive files such as system configuration data, authentication credentials, private keys, or other confidential information stored on the host. This risk is amplified by the fact that the utility's loader scripts are typically sourced from the guest image, making it difficult for administrators to detect malicious content. The vulnerability essentially creates a backdoor through which attackers can bypass normal file system access controls, potentially leading to complete system compromise if the host user has elevated privileges.
Mitigation strategies for CVE-2024-25940 should focus on implementing strict path restriction mechanisms within the bhyveload(8) utility and ensuring proper privilege separation during virtual machine boot processes. Administrators should immediately update their FreeBSD systems to versions that address this vulnerability through proper access control implementation. The recommended approach involves enforcing strict sandboxing of the loader environment, implementing mandatory access controls, and ensuring that host file system access is properly restricted during the boot process. Security practitioners should also consider implementing monitoring solutions that can detect unauthorized file access patterns during virtual machine boot operations, aligning with the ATT&CK technique T1078.004 for Valid Accounts and T1566.001 for Phishing. Additionally, organizations should review their virtualization security policies and ensure that the principle of least privilege is maintained when executing bhyveload(8) commands, particularly when running with elevated host privileges.