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GHSA-P79H-JCRM-6QRC

Vulnerability from github – Published: 2025-04-01 18:30 – Updated: 2025-11-03 21:33
VLAI
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 (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.

Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Show details on source website
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{
  "affected": [],
  "aliases": [
    "CVE-2025-21920"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-125"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2025-04-01T16:15:22Z",
    "severity": "HIGH"
  },
  "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\u0027t 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.",
  "id": "GHSA-p79h-jcrm-6qrc",
  "modified": "2025-11-03T21:33:23Z",
  "published": "2025-04-01T18:30:51Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-21920"
    },
    {
      "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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