CVE-2025-21920: Linux Kernel

High severity, CVSS 7.1. EPSS: 0.2% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: vlan: enforce underlying device type Currently, VLAN devices can be created on top of non-ethernet devices. Besides the fact that it doesn't make much sense, this also causes a bug which leaks the address of a kernel function to usermode. When creating a VLAN device, we initialize GARP (garp_init_applicant) and MRP (mrp_init_applicant) for the underlying device. As part of the initialization process, we add the multicast address of each applicant to the underlying device, by calling dev_mc_add. __dev_mc_add uses dev->addr_len to determine the length of the new multicast address. This causes an out-of-bounds read if dev->addr_len is greater than 6, since the multicast addresses provided by GARP and MRP are only 6 bytes long. This behaviour can be reproduced using the following commands: ip tunnel add gretest mode ip6gre local ::1 remote ::2 dev lo ip l set up dev gretest ip link add link gretest name vlantest type vlan id 100 Then, the following command will display the address of garp_pdu_rcv: ip maddr show | grep 01:80:c2:00:00:21 Fix the bug by enforcing the type of the underlying device during VLAN device initialization.

Affected products

• Linux Linux Kernel: from 2.6.35, before 5.4.291 (fixed in 5.4.291); from 5.5, before 5.10.235 (fixed in 5.10.235); from 5.11, before 5.15.179 (fixed in 5.15.179); from 5.16, before 6.1.131 (fixed in 6.1.131); from 6.2, before 6.6.83 (fixed in 6.6.83); from 6.7, before 6.12.19 (fixed in 6.12.19); …

Published 2025-04-01. Last modified 2026-06-17.