CVE-2017-16638 in vde
Summary
by MITRE
The Gentoo net-misc/vde package before version 2.3.2-r4 may allow members of the "qemu" group to gain root privileges by creating a hard link in a directory on which "chown" is called recursively by the OpenRC service script.
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Analysis
by VulDB Data Team • 12/04/2019
The vulnerability identified as CVE-2017-16638 resides within the Gentoo net-misc/vde package ecosystem, specifically affecting versions prior to 2.3.2-r4. This represents a privilege escalation flaw that exploits a design weakness in how file ownership is managed during the OpenRC service script execution process. The vulnerability is particularly concerning because it allows unprivileged users who belong to the "qemu" group to escalate their privileges to the root level, creating a significant security risk in virtualized environments where such groups are commonly utilized.
The technical flaw manifests through a race condition or directory traversal issue within the OpenRC service script that handles the vde package operations. When the service script executes "chown" commands recursively on directories, it fails to properly validate or secure the file system state, allowing an attacker with qemu group membership to manipulate the directory structure through hard link creation. This manipulation enables the attacker to effectively bypass normal permission controls and gain elevated privileges. The vulnerability stems from improper handling of file system operations and lacks adequate access control mechanisms during the recursive chown execution process, creating an exploitable path for privilege escalation.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can compromise the entire virtualization infrastructure that relies on the vde package for network virtualization. Attackers can leverage this flaw to gain root access to systems running virtualized environments, potentially leading to complete system compromise, data exfiltration, or further lateral movement within networked environments. The vulnerability affects systems where the vde package is used for virtual network management, particularly in cloud computing environments, container orchestration platforms, and virtual desktop infrastructures. This makes it a critical concern for organizations deploying virtualization technologies where qemu group membership might be granted to untrusted users or where the vde package is used in production environments.
Mitigation strategies for this vulnerability include immediate upgrade to version 2.3.2-r4 or later of the net-misc/vde package, which contains the necessary patches to address the directory traversal and recursive chown handling issues. System administrators should also implement proper access controls to limit qemu group membership to only trusted users and processes. The remediation process should include thorough auditing of existing systems to identify and remove any existing hard links that could be exploited, along with implementing monitoring solutions to detect unusual file system operations that might indicate exploitation attempts. This vulnerability aligns with CWE-284, which describes improper access control issues, and maps to attack patterns within the ATT&CK framework related to privilege escalation through local exploitation techniques. Organizations should also consider implementing the principle of least privilege and regularly reviewing group memberships to minimize potential attack vectors.