CVE-2016-1576 in Linux
Summary
by MITRE
The overlayfs implementation in the Linux kernel through 4.5.2 does not properly restrict the mount namespace, which allows local users to gain privileges by mounting an overlayfs filesystem on top of a FUSE filesystem, and then executing a crafted setuid program.
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Analysis
by VulDB Data Team • 11/30/2024
The vulnerability identified as CVE-2016-1576 represents a critical privilege escalation flaw within the Linux kernel's overlayfs implementation affecting versions through 4.5.2. This issue stems from improper handling of mount namespaces during overlayfs filesystem operations, creating a pathway for local attackers to elevate their privileges from standard user level to root access. The vulnerability specifically exploits the interaction between overlayfs and FUSE filesystems, leveraging the kernel's insufficient restrictions on mount namespace manipulation to bypass security controls that should prevent such privilege escalation.
The technical flaw manifests when an attacker mounts an overlayfs filesystem on top of an existing FUSE filesystem within the same mount namespace. This particular configuration creates a scenario where the overlayfs implementation fails to properly validate or restrict the namespace boundaries, allowing malicious operations to propagate through the filesystem layering mechanism. The vulnerability is particularly dangerous because it relies on the combination of overlayfs and FUSE filesystems, where overlayfs creates a layered filesystem view while FUSE provides user-space filesystem capabilities. When these two components interact improperly, the kernel's namespace isolation mechanisms are bypassed, enabling attackers to execute crafted setuid programs with elevated privileges.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with complete system control once exploited. Local users can leverage this flaw to gain root access without requiring physical presence or network connectivity, making it particularly dangerous in multi-user environments or systems where users have legitimate access to the system. The attack vector requires local access and the ability to mount filesystems, but these capabilities are often available to regular users in standard Linux environments, making the vulnerability widely exploitable. The privilege escalation occurs through the overlayfs mount operation that creates an environment where setuid binaries can be executed with root privileges, effectively bypassing the kernel's security model that normally prevents such operations.
Mitigation strategies for CVE-2016-1576 focus on both kernel-level patches and operational security measures. The primary fix involves updating to Linux kernel versions 4.5.3 or later, where the overlayfs implementation properly enforces namespace restrictions and prevents the specific attack pattern. System administrators should also implement restrictive mount options and disable unnecessary filesystem support where possible, particularly in environments where untrusted users have access. The vulnerability aligns with CWE-276, which addresses improper privilege management, and maps to attack techniques in the MITRE ATT&CK framework under privilege escalation and persistence mechanisms. Organizations should conduct thorough vulnerability assessments to identify systems running affected kernel versions and implement comprehensive patch management processes to address this and related filesystem security issues. Additionally, monitoring for unauthorized mount operations and filesystem layering activities can help detect potential exploitation attempts.