CVE-2016-9962 in Docker
Summary
by MITRE
RunC allowed additional container processes via 'runc exec' to be ptraced by the pid 1 of the container. This allows the main processes of the container, if running as root, to gain access to file-descriptors of these new processes during the initialization and can lead to container escapes or modification of runC state before the process is fully placed inside the container.
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Analysis
by VulDB Data Team • 10/28/2022
The vulnerability identified as CVE-2016-9962 affects the RunC container runtime component that forms a critical part of the docker container ecosystem. This flaw resides in how RunC handles process tracing capabilities during container execution, specifically when the runc exec command is utilized to launch additional processes within a container environment. The issue stems from insufficient isolation mechanisms that allow processes initiated through the exec command to maintain tracing capabilities that should be restricted to the container's primary process.
The technical implementation of this vulnerability exploits a fundamental flaw in the Linux process tracing subsystem integration within RunC's container management. When a new process is created using runc exec, the system fails to properly enforce the tracing restrictions that should prevent the container's pid 1 process from establishing ptrace relationships with these newly created processes. This misconfiguration enables the main container process to gain unauthorized access to file descriptors and memory spaces of the newly spawned processes during their initialization phase. The vulnerability specifically impacts containers running with root privileges where the pid 1 process has elevated permissions that can be leveraged for malicious activities.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential container escape scenarios and state manipulation within the RunC runtime itself. An attacker who controls the container's main process can exploit this weakness to access sensitive file descriptors of newly created processes, potentially gaining access to container resources, network connections, or even system-level capabilities that should remain isolated. The vulnerability creates a window of opportunity during process initialization where the container's security boundaries are temporarily weakened, allowing for unauthorized access to the runtime state and potentially enabling attackers to modify critical container configuration data before processes are fully isolated.
This vulnerability aligns with CWE-276, which addresses improper privilege management, and represents a specific case of inadequate process isolation in containerized environments. From an ATT&CK perspective, this flaw maps to techniques involving privilege escalation and container escape, specifically targeting the container runtime environment rather than the host system directly. The vulnerability demonstrates how container security mechanisms can be undermined through improper handling of Linux kernel features, particularly those related to process tracing and debugging capabilities. Organizations using RunC-based container solutions should consider implementing additional monitoring and access control measures to detect unauthorized ptrace operations and process tracing activities that could indicate exploitation attempts.
The remediation for this vulnerability requires updating RunC to versions that properly enforce process tracing restrictions and implement stricter isolation mechanisms for exec operations. System administrators should also implement monitoring solutions that can detect unauthorized ptrace activities within container environments and consider implementing additional security controls such as seccomp profiles and capability drops to limit the privileges available to container processes. The vulnerability underscores the importance of proper kernel feature handling in container security implementations and the need for comprehensive security testing of container runtime components against privilege escalation vectors.