{"id":"CVE-2025-21920","summary":"vlan: enforce underlying device type","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nvlan: enforce underlying device type\n\nCurrently, VLAN devices can be created on top of non-ethernet devices.\n\nBesides the fact that it doesn't make much sense, this also causes a\nbug which leaks the address of a kernel function to usermode.\n\nWhen creating a VLAN device, we initialize GARP (garp_init_applicant)\nand MRP (mrp_init_applicant) for the underlying device.\n\nAs part of the initialization process, we add the multicast address of\neach applicant to the underlying device, by calling dev_mc_add.\n\n__dev_mc_add uses dev-\u003eaddr_len to determine the length of the new\nmulticast address.\n\nThis causes an out-of-bounds read if dev-\u003eaddr_len is greater than 6,\nsince the multicast addresses provided by GARP and MRP are only 6\nbytes long.\n\nThis behaviour can be reproduced using the following commands:\n\nip tunnel add gretest mode ip6gre local ::1 remote ::2 dev lo\nip l set up dev gretest\nip link add link gretest name vlantest type vlan id 100\n\nThen, the following command will display the address of garp_pdu_rcv:\n\nip maddr show | grep 01:80:c2:00:00:21\n\nFix the bug by enforcing the type of the underlying device during VLAN\ndevice initialization.","modified":"2026-04-02T12:45:17.153353Z","published":"2025-04-01T15:40:54.595Z","related":["ALSA-2025:8643","SUSE-SU-2025:02249-1","SUSE-SU-2025:02254-1","SUSE-SU-2025:02307-1","SUSE-SU-2025:02333-1","SUSE-SU-2025:02334-1","SUSE-SU-2025:02335-1","SUSE-SU-2025:02538-1","SUSE-SU-2025:02923-1","SUSE-SU-2025:20475-1","SUSE-SU-2025:20483-1","SUSE-SU-2025:20493-1","SUSE-SU-2025:20498-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21920.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/0fb7aa04c19eac4417f360a9f7611a60637bdacc"},{"type":"WEB","url":"https://git.kernel.org/stable/c/30e8aee77899173a82ae5ed89f536c096f20aaeb"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3561442599804905c3defca241787cd4546e99a7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5a515d13e15536e82c5c7c83eb6cf5bc4827fee5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7f1564b2b2072b7aa1ac75350e9560a07c7a44fd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b33a534610067ade2bdaf2052900aaad99701353"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b6c72479748b7ea09f53ed64b223cee6463dc278"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fa40ebef69234e39ec2d26930d045f2fb9a8cb2b"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21920.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-21920"},{"type":"PACKAGE","url":"https://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/cve-osv-conversion/osv-output/CVE-2025-21920.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H"}]}