CVE-2025-21920 (GCVE-0-2025-21920)

Vulnerability from cvelistv5 – Published: 2025-04-01 15:40 – Updated: 2026-05-11 21:09
VLAI
Title
vlan: enforce underlying device type
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.
Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-10-01 20:07 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < 7f1564b2b2072b7aa1ac75350e9560a07c7a44fd (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < fa40ebef69234e39ec2d26930d045f2fb9a8cb2b (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < 0fb7aa04c19eac4417f360a9f7611a60637bdacc (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < 5a515d13e15536e82c5c7c83eb6cf5bc4827fee5 (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < 3561442599804905c3defca241787cd4546e99a7 (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < 30e8aee77899173a82ae5ed89f536c096f20aaeb (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < b6c72479748b7ea09f53ed64b223cee6463dc278 (git)
Affected: 22bedad3ce112d5ca1eaf043d4990fa2ed698c87 , < b33a534610067ade2bdaf2052900aaad99701353 (git)
guessed Create a notification for this product.
Linux Linux Affected: 2.6.35
Unaffected: 0 , < 2.6.35 (semver)
Unaffected: 5.4.291 , ≤ 5.4.* (semver)
Unaffected: 5.10.235 , ≤ 5.10.* (semver)
Unaffected: 5.15.179 , ≤ 5.15.* (semver)
Unaffected: 6.1.131 , ≤ 6.1.* (semver)
Unaffected: 6.6.83 , ≤ 6.6.* (semver)
Unaffected: 6.12.19 , ≤ 6.12.* (semver)
Unaffected: 6.13.7 , ≤ 6.13.* (semver)
Unaffected: 6.14 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "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."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: vlan: imponer el tipo de dispositivo subyacente Actualmente, los dispositivos VLAN se pueden crear sobre dispositivos que no sean Ethernet. Adem\u00e1s del hecho de que no tiene mucho sentido, esto tambi\u00e9n causa un error que filtra la direcci\u00f3n de una funci\u00f3n del kernel al modo de usuario. Al crear un dispositivo VLAN, inicializamos GARP (garp_init_applicant) y MRP (mrp_init_applicant) para el dispositivo subyacente. Como parte del proceso de inicializaci\u00f3n, agregamos la direcci\u00f3n de multidifusi\u00f3n de cada solicitante al dispositivo subyacente, llamando a dev_mc_add. __dev_mc_add usa dev-\u0026gt;addr_len para determinar la longitud de la nueva direcci\u00f3n de multidifusi\u00f3n. Esto causa una lectura fuera de los l\u00edmites si dev-\u0026gt;addr_len es mayor que 6, ya que las direcciones de multidifusi\u00f3n proporcionadas por GARP y MRP solo tienen 6 bytes de longitud. Este comportamiento se puede reproducir utilizando los siguientes comandos: 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 Luego, el siguiente comando mostrar\u00e1 la direcci\u00f3n de garp_pdu_rcv: ip maddr show | grep 01:80:c2:00:00:21 Corrija el error aplicando el tipo de dispositivo subyacente durante la inicializaci\u00f3n del dispositivo VLAN."
          }
        ],
        "id": "CVE-2025-21920",
        "lastModified": "2026-06-17T08:44:36.850",
        "metrics": {
          "cvssMetricV31": [
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              "cvssData": {
                "attackComplexity": "LOW",
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                "baseScore": 7.1,
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                "confidentialityImpact": "HIGH",
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                "scope": "UNCHANGED",
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    "redhat_vex": {
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      "current_release_date": "2026-06-30T00:05:23+00:00",
      "cve": "CVE-2025-21920",
      "id": "CVE-2025-21920",
      "initial_release_date": "2025-04-01T00:00:00+00:00",
      "product_status:fixed": "305",
      "product_status:known_affected": "188",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: vlan: enforce underlying device type",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-21920.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-23T00:46:48Z",
      "cve": "CVE-2025-21920",
      "id": "CVE-2025-21920",
      "initial_release_date": "2025-04-04T02:59:17Z",
      "product_status:known_affected": "788",
      "product_status:recommended": "476",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-21920",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-21920.json",
      "version": "53"
    },
    "vulnrichment": {
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              "dateUpdated": "2025-11-03T19:39:13.839Z",
              "orgId": "af854a3a-2127-422b-91ae-364da2661108",
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            "references": [
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                "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html"
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              {
                "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html"
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            ],
            "title": "CVE Program Container"
          },
          {
            "metrics": [
              {
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                  "attackComplexity": "LOW",
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                  "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
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              {
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                    "id": "CVE-2025-21920",
                    "options": [
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                      },
                      {
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                      },
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                      }
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              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
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        ],
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              "versions": [
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            }
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.