CVE-2017-17448 in Linux
Summary
by MITRE
net/netfilter/nfnetlink_cthelper.c in the Linux kernel through 4.14.4 does not require the CAP_NET_ADMIN capability for new, get, and del operations, which allows local users to bypass intended access restrictions because the nfnl_cthelper_list data structure is shared across all net namespaces.
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Analysis
by VulDB Data Team • 01/17/2023
The vulnerability identified as CVE-2017-17448 resides within the Linux kernel's netfilter subsystem, specifically in the nfnetlink_cthelper.c component. This flaw affects kernel versions through 4.14.4 and represents a significant privilege escalation risk that undermines the intended security boundaries of network namespaces. The issue stems from insufficient capability checks during critical operations on connection tracking helpers, which are essential components for managing network connections in the Linux kernel's packet filtering framework.
The technical root cause of this vulnerability lies in the improper implementation of access control mechanisms within the nfnl_cthelper_list data structure. This structure serves as a shared resource across all network namespaces, yet the kernel fails to enforce the required CAP_NET_ADMIN capability for fundamental operations including new, get, and del commands. This omission allows unprivileged local users to perform administrative actions on connection tracking helpers without proper authorization, effectively bypassing the kernel's intended access control policies.
The operational impact of this vulnerability is severe as it enables local privilege escalation attacks that can be exploited by any user with access to the system. An attacker can leverage this flaw to manipulate connection tracking helpers across different network namespaces, potentially disrupting network services, creating backdoors, or gaining elevated privileges. The shared nature of the nfnl_cthelper_list data structure means that modifications in one namespace can affect the entire system's network behavior, making this a particularly dangerous vulnerability for multi-tenant environments or systems where network isolation is critical.
This vulnerability maps to CWE-284 Access Control in the Common Weakness Enumeration catalog, specifically representing an insufficient privilege checks scenario where the kernel fails to validate that operations are performed by users with appropriate administrative capabilities. The ATT&CK framework categorizes this under privilege escalation techniques, specifically leveraging kernel vulnerabilities to gain elevated system privileges. The flaw demonstrates a classic case of improper privilege validation where the kernel's security model is bypassed through insufficient capability checks, allowing local users to perform actions typically restricted to privileged processes.
Mitigation strategies for CVE-2017-17448 include applying the relevant kernel security patches that implement proper CAP_NET_ADMIN capability checks for connection tracking helper operations. System administrators should ensure all Linux systems are updated to kernel versions that contain the fix, which typically involves adding explicit capability validation before allowing operations on the nfnl_cthelper_list data structure. Additionally, organizations should implement network segmentation and monitoring to detect anomalous connection tracking helper modifications, as well as maintain regular vulnerability assessments to identify similar privilege escalation vectors in the kernel's network subsystem. The fix typically involves modifying the kernel code to require CAP_NET_ADMIN capability for all operations on connection tracking helpers, thereby restoring the intended security boundaries between different network namespaces and preventing unauthorized access to critical network management functions.