CVE-2016-8649 in lxc
Summary
by MITRE
lxc-attach in LXC before 1.0.9 and 2.x before 2.0.6 allows an attacker inside of an unprivileged container to use an inherited file descriptor, of the host's /proc, to access the rest of the host's filesystem via the openat() family of syscalls.
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Analysis
by VulDB Data Team • 09/18/2024
The vulnerability CVE-2016-8649 represents a critical privilege escalation flaw in the Linux Containers (LXC) virtualization system affecting versions prior to 1.0.9 and 2.x prior to 2.0.6. This issue specifically targets the lxc-attach utility which is commonly used to attach to running containers. The flaw stems from improper handling of file descriptor inheritance during container attachment operations, creating a pathway for unprivileged container users to bypass container isolation mechanisms and access host filesystem resources.
The technical root cause involves the lxc-attach utility's failure to properly sanitize file descriptors inherited from the host process when executing within a container context. When an unprivileged user executes lxc-attach from within an unprivileged container, the utility inherits file descriptors from the host process that include access to /proc filesystem entries. This inherited access, combined with the openat() family of system calls, allows the attacker to traverse and access the host's filesystem through these inherited file descriptors. The vulnerability operates at the kernel level through the openat() syscall family which provides a mechanism for opening files relative to a directory file descriptor, enabling path traversal attacks against inherited descriptors.
From an operational perspective, this vulnerability creates a severe security risk as it allows local privilege escalation from container user to host system access. An attacker with access to an unprivileged container can leverage this flaw to read arbitrary files on the host system, potentially accessing sensitive information, configuration files, or even system credentials. The impact extends beyond simple information disclosure, as the attacker could potentially modify files, escalate privileges further, or establish persistent access to the host system. This vulnerability directly violates the fundamental security principle of container isolation and undermines the trust model that containerization systems rely upon for security boundaries.
The vulnerability aligns with CWE-276, which addresses improper privileges, and maps to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation'. The attack vector requires local access to an unprivileged container, making it particularly concerning for multi-tenant environments where container isolation is critical. Organizations using LXC containers should immediately upgrade to versions 1.0.9 or 2.0.6 and higher to mitigate this risk. Additional mitigations include implementing proper container security policies, restricting container capabilities, and monitoring for suspicious file access patterns. System administrators should also consider implementing mandatory access controls and regularly auditing container configurations to prevent unauthorized access to host resources. The vulnerability highlights the importance of proper file descriptor management in containerized environments and demonstrates the need for comprehensive security testing of container management utilities.