CVE-2026-39402 lxc lxc-user-nic insufficient ownership validation allows cross-tenant OVS port deletion

What is CVE-2026-39402?

CVE-2026-39402 is a medium-severity missing authorization vulnerability in lxc, published on 5 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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.

Weakness: CWE-863

Which versions are affected by CVE-2026-39402?

It affects 1 product.

Products include Linuxcontainers Lxc.

How do I fix CVE-2026-39402?

Upgrade to a fixed version.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

Is CVE-2026-39402 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39402 exists.

Other vulnerabilities in lxc

• CVE-2016-8649 Path traversal in LXC before 1.0.9 and 2.x before 2.0.6 Critical 9.1
• CVE-2016-10124 Privilege escalation in n/a High 8.6
• CVE-2017-18641 Supply chain in n/a High 8.1
• CVE-2013-6441 Privilege escalation in n/a High 7.2
• CVE-2015-1331 Path traversal in n/a Medium 4.9

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-39402, GHSA-3m9j-g9gc-vcvq, MGASA-2026-0172, OESA-2026-2657, UBUNTU-CVE-2026-39402, openSUSE-SU-2026:10678-1.