CVE-2026-39402: 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 ...

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.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

CVSS 4.0

4.3/10

CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.16%

5.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-863

Affected Software

Vendor	Product	Versions
Linuxcontainers	Lxc	< 7.0.0

References

https://github.com/lxc/lxc/security/advisories/GHSA-3m9j-g9gc-vcvqExploit, Vendor Advisory
https://github.com/lxc/lxc/security/advisories/GHSA-3m9j-g9gc-vcvqExploit, Vendor Advisory

Timeline

Published: May 5, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-39402?

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.

How severe is CVE-2026-39402?

CVE-2026-39402 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.16% probability of exploitation in the next 30 days.

How do I fix CVE-2026-39402?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.