CVE-2025-21920

Summary

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 Software

VendorProductVersion RangeStatus
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < 7f1564b2b2072b7aa1ac75350e9560a07c7a44fdaffected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < fa40ebef69234e39ec2d26930d045f2fb9a8cb2baffected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < 0fb7aa04c19eac4417f360a9f7611a60637bdaccaffected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < 5a515d13e15536e82c5c7c83eb6cf5bc4827fee5affected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < 3561442599804905c3defca241787cd4546e99a7affected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < 30e8aee77899173a82ae5ed89f536c096f20aaebaffected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < b6c72479748b7ea09f53ed64b223cee6463dc278affected
LinuxLinux22bedad3ce112d5ca1eaf043d4990fa2ed698c87 < b33a534610067ade2bdaf2052900aaad99701353affected
LinuxLinux2.6.35affected
LinuxLinux0 < 2.6.35unaffected
LinuxLinux5.4.291 <= 5.4.*unaffected
LinuxLinux5.10.235 <= 5.10.*unaffected
LinuxLinux5.15.179 <= 5.15.*unaffected
LinuxLinux6.1.131 <= 6.1.*unaffected
LinuxLinux6.6.83 <= 6.6.*unaffected
LinuxLinux6.12.19 <= 6.12.*unaffected
LinuxLinux6.13.7 <= 6.13.*unaffected
LinuxLinux6.14 <= *unaffected

Weaknesses

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

CVE Program Container

Additional References

References