CVE-2025-38248 (GCVE-0-2025-38248)
Vulnerability from cvelistv5
Published
2025-07-09 10:42
Modified
2025-07-28 04:16
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: bridge: mcast: Fix use-after-free during router port configuration The bridge maintains a global list of ports behind which a multicast router resides. The list is consulted during forwarding to ensure multicast packets are forwarded to these ports even if the ports are not member in the matching MDB entry. When per-VLAN multicast snooping is enabled, the per-port multicast context is disabled on each port and the port is removed from the global router port list: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 # ip link add name dummy1 up master br1 type dummy # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 1 $ bridge -d mdb show | grep router However, the port can be re-added to the global list even when per-VLAN multicast snooping is enabled: # ip link set dev dummy1 type bridge_slave mcast_router 0 # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 Since commit 4b30ae9adb04 ("net: bridge: mcast: re-implement br_multicast_{enable, disable}_port functions"), when per-VLAN multicast snooping is enabled, multicast disablement on a port will disable the per-{port, VLAN} multicast contexts and not the per-port one. As a result, a port will remain in the global router port list even after it is deleted. This will lead to a use-after-free [1] when the list is traversed (when adding a new port to the list, for example): # ip link del dev dummy1 # ip link add name dummy2 up master br1 type dummy # ip link set dev dummy2 type bridge_slave mcast_router 2 Similarly, stale entries can also be found in the per-VLAN router port list. When per-VLAN multicast snooping is disabled, the per-{port, VLAN} contexts are disabled on each port and the port is removed from the per-VLAN router port list: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1 # ip link add name dummy1 up master br1 type dummy # bridge vlan add vid 2 dev dummy1 # bridge vlan global set vid 2 dev br1 mcast_snooping 1 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 0 $ bridge vlan global show dev br1 vid 2 | grep router However, the port can be re-added to the per-VLAN list even when per-VLAN multicast snooping is disabled: # bridge vlan set vid 2 dev dummy1 mcast_router 0 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 When the VLAN is deleted from the port, the per-{port, VLAN} multicast context will not be disabled since multicast snooping is not enabled on the VLAN. As a result, the port will remain in the per-VLAN router port list even after it is no longer member in the VLAN. This will lead to a use-after-free [2] when the list is traversed (when adding a new port to the list, for example): # ip link add name dummy2 up master br1 type dummy # bridge vlan add vid 2 dev dummy2 # bridge vlan del vid 2 dev dummy1 # bridge vlan set vid 2 dev dummy2 mcast_router 2 Fix these issues by removing the port from the relevant (global or per-VLAN) router port list in br_multicast_port_ctx_deinit(). The function is invoked during port deletion with the per-port multicast context and during VLAN deletion with the per-{port, VLAN} multicast context. Note that deleting the multicast router timer is not enough as it only takes care of the temporary multicast router states (1 or 3) and not the permanent one (2). [1] BUG: KASAN: slab-out-of-bounds in br_multicast_add_router.part.0+0x3f1/0x560 Write of size 8 at addr ffff888004a67328 by task ip/384 [...] Call Trace: <TASK> dump_stack ---truncated---
References
Impacted products
Vendor Product Version
Linux Linux Version: 2796d846d74a18cc6563e96eff8bf28c5e06f912
Version: 2796d846d74a18cc6563e96eff8bf28c5e06f912
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/bridge/br_multicast.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f05a4f9e959e0fc098046044c650acf897ea52d2",
              "status": "affected",
              "version": "2796d846d74a18cc6563e96eff8bf28c5e06f912",
              "versionType": "git"
            },
            {
              "lessThan": "7544f3f5b0b58c396f374d060898b5939da31709",
              "status": "affected",
              "version": "2796d846d74a18cc6563e96eff8bf28c5e06f912",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/bridge/br_multicast.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.15"
            },
            {
              "lessThan": "5.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.15.*",
              "status": "unaffected",
              "version": "6.15.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.16",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.15.5",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.16",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbridge: mcast: Fix use-after-free during router port configuration\n\nThe bridge maintains a global list of ports behind which a multicast\nrouter resides. The list is consulted during forwarding to ensure\nmulticast packets are forwarded to these ports even if the ports are not\nmember in the matching MDB entry.\n\nWhen per-VLAN multicast snooping is enabled, the per-port multicast\ncontext is disabled on each port and the port is removed from the global\nrouter port list:\n\n # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1\n # ip link add name dummy1 up master br1 type dummy\n # ip link set dev dummy1 type bridge_slave mcast_router 2\n $ bridge -d mdb show | grep router\n router ports on br1: dummy1\n # ip link set dev br1 type bridge mcast_vlan_snooping 1\n $ bridge -d mdb show | grep router\n\nHowever, the port can be re-added to the global list even when per-VLAN\nmulticast snooping is enabled:\n\n # ip link set dev dummy1 type bridge_slave mcast_router 0\n # ip link set dev dummy1 type bridge_slave mcast_router 2\n $ bridge -d mdb show | grep router\n router ports on br1: dummy1\n\nSince commit 4b30ae9adb04 (\"net: bridge: mcast: re-implement\nbr_multicast_{enable, disable}_port functions\"), when per-VLAN multicast\nsnooping is enabled, multicast disablement on a port will disable the\nper-{port, VLAN} multicast contexts and not the per-port one. As a\nresult, a port will remain in the global router port list even after it\nis deleted. This will lead to a use-after-free [1] when the list is\ntraversed (when adding a new port to the list, for example):\n\n # ip link del dev dummy1\n # ip link add name dummy2 up master br1 type dummy\n # ip link set dev dummy2 type bridge_slave mcast_router 2\n\nSimilarly, stale entries can also be found in the per-VLAN router port\nlist. When per-VLAN multicast snooping is disabled, the per-{port, VLAN}\ncontexts are disabled on each port and the port is removed from the\nper-VLAN router port list:\n\n # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1\n # ip link add name dummy1 up master br1 type dummy\n # bridge vlan add vid 2 dev dummy1\n # bridge vlan global set vid 2 dev br1 mcast_snooping 1\n # bridge vlan set vid 2 dev dummy1 mcast_router 2\n $ bridge vlan global show dev br1 vid 2 | grep router\n       router ports: dummy1\n # ip link set dev br1 type bridge mcast_vlan_snooping 0\n $ bridge vlan global show dev br1 vid 2 | grep router\n\nHowever, the port can be re-added to the per-VLAN list even when\nper-VLAN multicast snooping is disabled:\n\n # bridge vlan set vid 2 dev dummy1 mcast_router 0\n # bridge vlan set vid 2 dev dummy1 mcast_router 2\n $ bridge vlan global show dev br1 vid 2 | grep router\n       router ports: dummy1\n\nWhen the VLAN is deleted from the port, the per-{port, VLAN} multicast\ncontext will not be disabled since multicast snooping is not enabled\non the VLAN. As a result, the port will remain in the per-VLAN router\nport list even after it is no longer member in the VLAN. This will lead\nto a use-after-free [2] when the list is traversed (when adding a new\nport to the list, for example):\n\n # ip link add name dummy2 up master br1 type dummy\n # bridge vlan add vid 2 dev dummy2\n # bridge vlan del vid 2 dev dummy1\n # bridge vlan set vid 2 dev dummy2 mcast_router 2\n\nFix these issues by removing the port from the relevant (global or\nper-VLAN) router port list in br_multicast_port_ctx_deinit(). The\nfunction is invoked during port deletion with the per-port multicast\ncontext and during VLAN deletion with the per-{port, VLAN} multicast\ncontext.\n\nNote that deleting the multicast router timer is not enough as it only\ntakes care of the temporary multicast router states (1 or 3) and not the\npermanent one (2).\n\n[1]\nBUG: KASAN: slab-out-of-bounds in br_multicast_add_router.part.0+0x3f1/0x560\nWrite of size 8 at addr ffff888004a67328 by task ip/384\n[...]\nCall Trace:\n \u003cTASK\u003e\n dump_stack\n---truncated---"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-07-28T04:16:09.338Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f05a4f9e959e0fc098046044c650acf897ea52d2"
        },
        {
          "url": "https://git.kernel.org/stable/c/7544f3f5b0b58c396f374d060898b5939da31709"
        }
      ],
      "title": "bridge: mcast: Fix use-after-free during router port configuration",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38248",
    "datePublished": "2025-07-09T10:42:29.133Z",
    "dateReserved": "2025-04-16T04:51:23.997Z",
    "dateUpdated": "2025-07-28T04:16:09.338Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-38248\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-07-09T11:15:26.963\",\"lastModified\":\"2025-07-10T13:17:30.017\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nbridge: mcast: Fix use-after-free during router port configuration\\n\\nThe bridge maintains a global list of ports behind which a multicast\\nrouter resides. The list is consulted during forwarding to ensure\\nmulticast packets are forwarded to these ports even if the ports are not\\nmember in the matching MDB entry.\\n\\nWhen per-VLAN multicast snooping is enabled, the per-port multicast\\ncontext is disabled on each port and the port is removed from the global\\nrouter port list:\\n\\n # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1\\n # ip link add name dummy1 up master br1 type dummy\\n # ip link set dev dummy1 type bridge_slave mcast_router 2\\n $ bridge -d mdb show | grep router\\n router ports on br1: dummy1\\n # ip link set dev br1 type bridge mcast_vlan_snooping 1\\n $ bridge -d mdb show | grep router\\n\\nHowever, the port can be re-added to the global list even when per-VLAN\\nmulticast snooping is enabled:\\n\\n # ip link set dev dummy1 type bridge_slave mcast_router 0\\n # ip link set dev dummy1 type bridge_slave mcast_router 2\\n $ bridge -d mdb show | grep router\\n router ports on br1: dummy1\\n\\nSince commit 4b30ae9adb04 (\\\"net: bridge: mcast: re-implement\\nbr_multicast_{enable, disable}_port functions\\\"), when per-VLAN multicast\\nsnooping is enabled, multicast disablement on a port will disable the\\nper-{port, VLAN} multicast contexts and not the per-port one. As a\\nresult, a port will remain in the global router port list even after it\\nis deleted. This will lead to a use-after-free [1] when the list is\\ntraversed (when adding a new port to the list, for example):\\n\\n # ip link del dev dummy1\\n # ip link add name dummy2 up master br1 type dummy\\n # ip link set dev dummy2 type bridge_slave mcast_router 2\\n\\nSimilarly, stale entries can also be found in the per-VLAN router port\\nlist. When per-VLAN multicast snooping is disabled, the per-{port, VLAN}\\ncontexts are disabled on each port and the port is removed from the\\nper-VLAN router port list:\\n\\n # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1\\n # ip link add name dummy1 up master br1 type dummy\\n # bridge vlan add vid 2 dev dummy1\\n # bridge vlan global set vid 2 dev br1 mcast_snooping 1\\n # bridge vlan set vid 2 dev dummy1 mcast_router 2\\n $ bridge vlan global show dev br1 vid 2 | grep router\\n       router ports: dummy1\\n # ip link set dev br1 type bridge mcast_vlan_snooping 0\\n $ bridge vlan global show dev br1 vid 2 | grep router\\n\\nHowever, the port can be re-added to the per-VLAN list even when\\nper-VLAN multicast snooping is disabled:\\n\\n # bridge vlan set vid 2 dev dummy1 mcast_router 0\\n # bridge vlan set vid 2 dev dummy1 mcast_router 2\\n $ bridge vlan global show dev br1 vid 2 | grep router\\n       router ports: dummy1\\n\\nWhen the VLAN is deleted from the port, the per-{port, VLAN} multicast\\ncontext will not be disabled since multicast snooping is not enabled\\non the VLAN. As a result, the port will remain in the per-VLAN router\\nport list even after it is no longer member in the VLAN. This will lead\\nto a use-after-free [2] when the list is traversed (when adding a new\\nport to the list, for example):\\n\\n # ip link add name dummy2 up master br1 type dummy\\n # bridge vlan add vid 2 dev dummy2\\n # bridge vlan del vid 2 dev dummy1\\n # bridge vlan set vid 2 dev dummy2 mcast_router 2\\n\\nFix these issues by removing the port from the relevant (global or\\nper-VLAN) router port list in br_multicast_port_ctx_deinit(). The\\nfunction is invoked during port deletion with the per-port multicast\\ncontext and during VLAN deletion with the per-{port, VLAN} multicast\\ncontext.\\n\\nNote that deleting the multicast router timer is not enough as it only\\ntakes care of the temporary multicast router states (1 or 3) and not the\\npermanent one (2).\\n\\n[1]\\nBUG: KASAN: slab-out-of-bounds in br_multicast_add_router.part.0+0x3f1/0x560\\nWrite of size 8 at addr ffff888004a67328 by task ip/384\\n[...]\\nCall Trace:\\n \u003cTASK\u003e\\n dump_stack\\n---truncated---\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: bridge: mcast: Arreglar el use-after-free durante la configuraci\u00f3n del puerto del enrutador El puente mantiene una lista global de puertos tras los cuales reside un enrutador de multidifusi\u00f3n. La lista se consulta durante el reenv\u00edo para garantizar que los paquetes de multidifusi\u00f3n se reenv\u00eden a estos puertos incluso si los puertos no son miembros de la entrada MDB correspondiente. Cuando se habilita la vigilancia de multidifusi\u00f3n por VLAN, se deshabilita el contexto de multidifusi\u00f3n por puerto en cada puerto y el puerto se elimina de la lista global de puertos del enrutador: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 # ip link add name dummy1 up master br1 type dummy # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 1 $ bridge -d mdb show | grep router Sin embargo, el puerto se puede volver a agregar a la lista global incluso cuando el snooping de multidifusi\u00f3n por VLAN est\u00e1 habilitado: # ip link set dev dummy1 type bridge_slave mcast_router 0 # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 Desde el commit 4b30ae9adb04 (\\\"net: bridge: mcast: re-implement br_multicast_{enable, disabled}_port functions\\\"), cuando el snooping de multidifusi\u00f3n por VLAN est\u00e1 habilitado, la deshabilitaci\u00f3n de multidifusi\u00f3n en un puerto deshabilitar\u00e1 los contextos de multidifusi\u00f3n por {puerto, VLAN} y no el de cada puerto. Como resultado, un puerto permanecer\u00e1 en la lista global de puertos del enrutador incluso despu\u00e9s de eliminarlo. Esto generar\u00e1 un use-after-free [1] cuando se recorra la lista (al agregar un nuevo puerto a la lista, por ejemplo): # ip link del dev dummy1 # ip link add name dummy2 up master br1 type dummy # ip link set dev dummy2 type bridge_slave mcast_router 2 De manera similar, tambi\u00e9n se pueden encontrar entradas obsoletas en la lista de puertos del enrutador por VLAN. Cuando la vigilancia de multidifusi\u00f3n por VLAN est\u00e1 deshabilitada, los contextos por {puerto, VLAN} se deshabilitan en cada puerto y el puerto se elimina de la lista de puertos del enrutador por VLAN: # ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1 # ip link add name dummy1 up master br1 type dummy # bridge vlan add vid 2 dev dummy1 # bridge vlan global set vid 2 dev br1 mcast_snooping 1 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 0 $ bridge vlan global show dev br1 vid 2 | grep router Sin embargo, el puerto se puede volver a agregar a la lista por VLAN incluso cuando el snooping de multidifusi\u00f3n por VLAN est\u00e1 deshabilitado: # bridge vlan set vid 2 dev dummy1 mcast_router 0 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 Cuando se elimina la VLAN del puerto, el contexto de multidifusi\u00f3n por {puerto, VLAN} no se deshabilitar\u00e1 ya que el snooping de multidifusi\u00f3n no est\u00e1 habilitado en la VLAN. Como resultado, el puerto permanecer\u00e1 en la lista de puertos del enrutador por VLAN incluso despu\u00e9s de que ya no sea miembro de la VLAN. Esto dar\u00e1 lugar a un use-after-free [2] cuando se recorra la lista (al a\u00f1adir un nuevo puerto a la lista, por ejemplo): # ip link add name dummy2 up master br1 type dummy # bridge vlan add vid 2 dev dummy2 # bridge vlan del vid 2 dev dummy1 # bridge vlan set vid 2 dev dummy2 mcast_router 2 Solucione estos problemas eliminando el puerto de la lista de puertos del enrutador relevante (global o por VLAN) en br_multicast_port_ctx_deinit(). La funci\u00f3n se invoca durante la eliminaci\u00f3n del puerto con el contexto de multidifusi\u00f3n por puerto y durante la eliminaci\u00f3n de VLAN con el contexto de multidifusi\u00f3n por {puerto, VLAN}. ---truncado---\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/7544f3f5b0b58c396f374d060898b5939da31709\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f05a4f9e959e0fc098046044c650acf897ea52d2\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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