CVE-2025-21920

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Source
https://cve.org/CVERecord?id=CVE-2025-21920
Import Source
https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2025-21920.json
JSON Data
https://api.test.osv.dev/v1/vulns/CVE-2025-21920
Downstream
Related
Published
2025-04-01T15:40:54.595Z
Modified
2026-03-20T12:41:15.371684Z
Severity
  • 7.1 (High) CVSS_V3 - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H CVSS Calculator
Summary
vlan: enforce underlying device type
Details

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 (garpinitapplicant) and MRP (mrpinitapplicant) for the underlying device.

As part of the initialization process, we add the multicast address of each applicant to the underlying device, by calling devmcadd.

_devmcadd uses dev->addrlen 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 garppdurcv:

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.

Database specific 
{
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21920.json",
    "cna_assigner": "Linux"
}
References

Affected packages

Git / git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

Affected ranges

Type
GIT
Repo
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Events
Introduced
22bedad3ce112d5ca1eaf043d4990fa2ed698c87
Fixed
7f1564b2b2072b7aa1ac75350e9560a07c7a44fd
Fixed
fa40ebef69234e39ec2d26930d045f2fb9a8cb2b
Fixed
0fb7aa04c19eac4417f360a9f7611a60637bdacc
Fixed
5a515d13e15536e82c5c7c83eb6cf5bc4827fee5
Fixed
3561442599804905c3defca241787cd4546e99a7
Fixed
30e8aee77899173a82ae5ed89f536c096f20aaeb
Fixed
b6c72479748b7ea09f53ed64b223cee6463dc278
Fixed
b33a534610067ade2bdaf2052900aaad99701353

Database specific

source 
"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2025-21920.json"