lxc up to 6.x find_line authorization

Summaryinfo

A vulnerability classified as problematic was found in lxc up to 6.x. Impacted is the function find_line. Such manipulation leads to authorization. This vulnerability is documented as CVE-2026-39402. The attack needs to be performed locally. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in lxc up to 6.x and classified as problematic. Affected by this issue is the function find_line. The manipulation with an unknown input leads to a authorization vulnerability. Using CWE to declare the problem leads to CWE-863. The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions. Impacted is availability. CVE summarizes:

lxc is a Linux container runtime. In the setuid helper lxc-user-nic, the delete path contains a logic flaw in the find_line() function that allows an unprivileged user to delete OVS-attached network interfaces belonging to other users. When lxc-user-nic delete scans its NIC database to authorize a deletion request, the interface name comparison can set the authorization flag based on a name match alone, even when the ownership, type, and link fields in that database entry belong to a different user. The vulnerable check sits after the goto next label handling, meaning it is reachable on lines where earlier ownership checks failed or were skipped. Because nothing downstream of this authorization signal re-verifies that the matched database line actually belongs to the caller, an unprivileged attacker with a valid lxc-usernet policy entry can trigger deletion of another user's OVS port on the same bridge. This is limited to multi-tenant environments using lxc-user-nic with OpenVSwitch bridges. The impact is denial of service - one tenant can repeatedly disconnect networking from containers run by another tenant on shared infrastructure. This is patched in version 7.0.0.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-39402 since 04/07/2026. The exploitation is known to be easy. The attack needs to be approached locally. There are known technical details, but no exploit is available.

Upgrading to version 7.0.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-27497). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Name

• lxc

Version

• 6.x

Website

• Product: https://github.com/lxc/lxc/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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