CVE-2026-72061 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net: sit: require CAP_NET_ADMIN in the device netns for changelink
ipip6_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 ipip6_changelink() on rtnl_dev_link_net_capable() at its top, before any attribute is parsed. sit was the one tunnel type not covered by the recent series that added this check to the other changelink() handlers.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability represents a privilege escalation issue within the Linux kernel's networking subsystem, specifically affecting the sit (Simple Internet Tunnel) implementation. The flaw exists in the ipip6_changelink() function which manages network tunnel configuration changes, creating a dangerous scenario where an attacker with sufficient privileges in one network namespace can manipulate tunnels located in different namespaces. The vulnerability stems from an inconsistent security check pattern that fails to properly validate administrative capabilities across multiple network namespaces during tunnel link modifications.
The technical implementation flaw occurs because the rtnl changelink pathway only verifies CAP_NET_ADMIN permissions against the device's current network namespace dev_net(dev) without ensuring equivalent privileges exist in the target tunnel's network namespace t->net. This creates a privilege separation gap where a malicious user can leverage their administrative rights in one namespace to modify objects residing in another namespace, effectively bypassing intended security boundaries. The issue specifically affects IPv6 tunnel implementations where the function operates across at most two distinct network namespaces, making it particularly dangerous for containerized environments and multi-tenant systems where network isolation is critical.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables attackers to potentially manipulate network tunnel configurations in ways that could disrupt services, create unauthorized access paths, or establish persistent backdoors within network infrastructure. When a device is created or moved to a different network namespace from where the request originates, the existing security model fails to account for cross-namespace privilege validation, allowing attackers to modify tunnel parameters, change routing behavior, or even redirect traffic through maliciously configured tunnels. This represents a significant concern for cloud environments and systems employing network virtualization where proper namespace isolation is fundamental to security.
The mitigation strategy involves implementing a comprehensive CAP_NET_ADMIN check at the entry point of ipip6_changelink() using the rtnl_dev_link_net_capable() function before any attribute parsing occurs. This approach aligns with established security patterns that have been applied to other changelink() handlers within the kernel, ensuring consistent privilege validation across all tunnel types. The fix requires gating access to the tunnel configuration change function based on proper administrative capabilities in both involved network namespaces rather than just the current execution context. This solution addresses the root cause by enforcing strict namespace-based privilege checks that prevent unauthorized modifications of network objects across namespace boundaries, thereby maintaining the integrity of network isolation mechanisms and preventing potential lateral movement attacks.
This vulnerability classification aligns with CWE-276 (Insecure Default Permissions) and CWE-284 (Improper Access Control) while mapping to ATT&CK technique T1068 (Local Privilege Escalation) and T1566 (Phishing) through potential exploitation pathways. The fix demonstrates proper adherence to the principle of least privilege by ensuring that administrative actions are validated against all relevant security contexts rather than assuming uniform permissions across namespace boundaries. This represents a critical security enhancement for Linux systems, particularly those implementing containerization technologies or network virtualization where proper namespace isolation is essential for maintaining system integrity and preventing unauthorized network modifications.