CVE-2026-72051 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net: ip6_tunnel: require CAP_NET_ADMIN in the device netns for changelink
ip6_tnl_changelink() operates on at most two netns, dev_net(dev) and the tunnel link netns t->net. They differ once the device is created in or moved to a netns other than the one the request runs in. The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev), so a caller privileged there but not in t->net can rewrite a tunnel that lives in t->net.
Gate ip6_tnl_changelink() on rtnl_dev_link_net_capable() at its top, before any attribute is parsed.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described involves a privilege escalation issue within the Linux kernel's IPv6 tunneling subsystem specifically affecting the ip6_tunnel module. This flaw stems from an improper capability check during network device configuration changes, creating a potential security loophole that could be exploited by malicious actors with limited privileges. The vulnerability exists in the ip6_tnl_changelink() function which handles link layer operations for IPv6 tunnels, and it manifests when devices are moved between network namespaces where different privilege requirements apply.
The technical implementation flaw occurs because the kernel's rtnl (real-time netlink) changelink pathway performs capability verification only against the device's current network namespace dev_net(dev) rather than checking both the source and target network namespaces involved in the operation. This discrepancy allows an attacker with CAP_NET_ADMIN privileges in one namespace to manipulate tunnel configurations that exist within a different network namespace where they lack appropriate permissions. The function operates on at most two network namespaces - the device's current namespace and the tunnel link namespace - but only validates capabilities against one of them, creating a privilege separation gap.
The operational impact of this vulnerability extends beyond simple privilege escalation as it affects the fundamental security model of Linux network namespaces. An attacker could potentially manipulate IPv6 tunnel configurations across namespace boundaries, leading to possible man-in-the-middle attacks, network isolation bypasses, or disruption of network services. This issue particularly impacts systems running IPv6 tunneling applications where network namespaces are used for security isolation, such as containerized environments, virtualization platforms, or multi-tenant network deployments.
The mitigation strategy involves implementing a comprehensive capability check at the entry point of the ip6_tnl_changelink() function using the rtnl_dev_link_net_capable() helper. This approach ensures that proper authorization checks occur before any attribute parsing begins, effectively preventing unauthorized modifications to tunnel configurations across namespace boundaries. By gating the entire function on network namespace capabilities, the kernel enforces consistent privilege validation across all operations regardless of where the device or tunnel resides within the network namespace hierarchy.
This vulnerability aligns with CWE-284 (Improper Access Control) and relates to ATT&CK technique T1068 (Local Privilege Escalation) through the improper capability checking mechanism. The fix addresses a fundamental flaw in Linux kernel security model implementation where namespace boundaries are not properly enforced during device configuration changes, particularly affecting network administration operations that span multiple namespaces. This represents a critical security enhancement for systems relying on network namespace isolation for security purposes.
The solution follows established kernel security patterns by implementing early validation checks before resource manipulation occurs, preventing potential privilege escalation attacks that could compromise network integrity and isolation properties. This change ensures that all network device configuration modifications respect the proper namespace boundaries and capability requirements, maintaining the security guarantees provided by Linux network namespaces while preserving legitimate administrative functionality.