CVE-2017-17449 in Linux
Summary
by MITRE
The __netlink_deliver_tap_skb function in net/netlink/af_netlink.c in the Linux kernel through 4.14.4, when CONFIG_NLMON is enabled, does not restrict observations of Netlink messages to a single net namespace, which allows local users to obtain sensitive information by leveraging the CAP_NET_ADMIN capability to sniff an nlmon interface for all Netlink activity on the system.
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Analysis
by VulDB Data Team • 01/17/2023
The vulnerability identified as CVE-2017-17449 represents a significant information disclosure flaw in the Linux kernel's netlink subsystem, specifically within the __netlink_deliver_tap_skb function located in net/netlink/af_netlink.c. This issue affects Linux kernel versions through 4.14.4 and manifests when the CONFIG_NLMON kernel configuration option is enabled, creating a privilege escalation vector that allows local attackers to access sensitive system information through improper namespace isolation. The flaw fundamentally stems from the kernel's failure to properly restrict Netlink message observations to individual network namespaces, enabling unauthorized access to system-wide Netlink activity.
The technical implementation of this vulnerability occurs through the nlmon interface, which serves as a monitoring tool for Netlink messages within the Linux kernel. When CONFIG_NLMON is enabled, the kernel provides a mechanism for capturing and analyzing Netlink traffic, but the implementation lacks proper namespace boundaries that should normally isolate network communication between different namespaces. This oversight allows a local user with the CAP_NET_ADMIN capability to establish a monitoring interface that captures Netlink messages from all network namespaces on the system rather than being restricted to their own namespace. The vulnerability is particularly concerning because it enables passive information gathering without requiring elevated privileges beyond what is already granted through the CAP_NET_ADMIN capability.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with comprehensive visibility into system network operations and kernel communication patterns. An attacker with local access and CAP_NET_ADMIN capability can monitor all Netlink activity across the entire system, potentially exposing sensitive kernel data, network configuration information, routing tables, and other system-level communications that should normally be isolated within their respective network namespaces. This capability allows for reconnaissance activities that could reveal system architecture, identify running processes, and gather intelligence about kernel operations that could be leveraged in subsequent attacks. The vulnerability essentially creates a backdoor for monitoring system-wide kernel communication that bypasses normal security boundaries.
The security implications of this flaw align with CWE-200, which addresses improper information exposure, and can be mapped to ATT&CK technique T1083, which covers file and directory discovery, as the vulnerability enables unauthorized access to system information that would normally be protected by namespace isolation. The vulnerability demonstrates a critical failure in kernel security architecture where proper isolation mechanisms are bypassed, creating a pathway for information leakage that violates fundamental security principles of compartmentalization and least privilege. Organizations running affected kernel versions are particularly vulnerable because the attack requires minimal privileges beyond what is already granted to network administrators, making it accessible to users with legitimate network management capabilities.
Mitigation strategies for this vulnerability primarily involve updating to kernel versions that contain the appropriate patches, which typically address the namespace isolation issue by properly enforcing boundaries between network namespaces when processing Netlink messages. System administrators should also consider disabling the CONFIG_NLMON option if Netlink monitoring functionality is not required in their environments, as this removes the attack surface entirely. Additionally, implementing proper privilege management and limiting the assignment of CAP_NET_ADMIN capability to only those users who absolutely require it can reduce the risk exposure. Network monitoring solutions should also be configured to properly isolate Netlink traffic and implement additional filtering mechanisms to prevent unauthorized access to system-level communication data. The patch for this vulnerability specifically addresses the namespace boundary enforcement in the netlink subsystem, ensuring that Netlink message observations are properly restricted to individual network namespaces rather than allowing cross-namespace monitoring.