CVE-2026-74615 (GCVE-0-2026-74615)
Vulnerability from cvelistv5
Published
2026-08-22 15:32
Modified
2026-08-25 05:40
Severity ?
8.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: vxlan: do not arm the ageing timer on a device that is down vxlan_changelink() arms vxlan->age_timer whenever the requested ageing interval differs from the configured one: if (conf.age_interval != vxlan->cfg.age_interval) mod_timer(&vxlan->age_timer, jiffies); There is no netif_running() test, so the timer is armed even on a device that was never brought up. The only synchronous cancel in the driver is the timer_delete_sync() in vxlan_stop(), which is .ndo_stop. netif_close_many() drops devices without IFF_UP before __dev_close_many() runs, so that cancel is skipped for such a device. vxlan_setup() sets dev->needs_free_netdev = true and age_timer is a member of struct vxlan_dev, so free_netdev() releases the allocation the timer lives in while it is still queued on a timer_base. expire_timers() unlinks the entry before it loads timer->function, so the timer core writes through the freed object's list pointers: BUG: KASAN: slab-use-after-free in __run_timers+0x208/0x654 Write of size 8 at addr ffff00001adace68 by task true/192 __asan_store8+0x84/0xac __run_timers+0x208/0x654 run_timer_softirq+0x154/0x18c Allocated by task 189: alloc_netdev_mqs+0x64/0x720 rtnl_create_link+0x4ac/0x520 rtnl_newlink+0x758/0xd00 Freed by task 191: netdev_release+0x40/0x58 netdev_run_todo+0x4a4/0x8c0 rtnl_dellink+0x200/0x4e8 The rtnl operations involved are netns-scoped, so an unprivileged user can perform them in a new user and network namespace. Arming the timer on a down device never had an effect: vxlan_cleanup() returns early on !netif_running(), and vxlan_open() arms the timer for any non-zero interval once the device is brought up. Add the missing test. Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>
References
Impacted products
Vendor Product Version
Linux Linux Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
Version: 40051c4dcad5b374156ad9cceae8d15c0ef1cb95
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{
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/vxlan/vxlan_core.c"
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nvxlan: do not arm the ageing timer on a device that is down\n\nvxlan_changelink() arms vxlan-\u003eage_timer whenever the requested ageing\ninterval differs from the configured one:\n\n\tif (conf.age_interval != vxlan-\u003ecfg.age_interval)\n\t\tmod_timer(\u0026vxlan-\u003eage_timer, jiffies);\n\nThere is no netif_running() test, so the timer is armed even on a device\nthat was never brought up.  The only synchronous cancel in the driver is\nthe timer_delete_sync() in vxlan_stop(), which is .ndo_stop.\nnetif_close_many() drops devices without IFF_UP before\n__dev_close_many() runs, so that cancel is skipped for such a device.\n\nvxlan_setup() sets dev-\u003eneeds_free_netdev = true and age_timer is a\nmember of struct vxlan_dev, so free_netdev() releases the allocation the\ntimer lives in while it is still queued on a timer_base.\nexpire_timers() unlinks the entry before it loads timer-\u003efunction, so\nthe timer core writes through the freed object\u0027s list pointers:\n\n  BUG: KASAN: slab-use-after-free in __run_timers+0x208/0x654\n  Write of size 8 at addr ffff00001adace68 by task true/192\n   __asan_store8+0x84/0xac\n   __run_timers+0x208/0x654\n   run_timer_softirq+0x154/0x18c\n  Allocated by task 189:\n   alloc_netdev_mqs+0x64/0x720\n   rtnl_create_link+0x4ac/0x520\n   rtnl_newlink+0x758/0xd00\n  Freed by task 191:\n   netdev_release+0x40/0x58\n   netdev_run_todo+0x4a4/0x8c0\n   rtnl_dellink+0x200/0x4e8\n\nThe rtnl operations involved are netns-scoped, so an unprivileged user\ncan perform them in a new user and network namespace.\n\nArming the timer on a down device never had an effect: vxlan_cleanup()\nreturns early on !netif_running(), and vxlan_open() arms the timer for\nany non-zero interval once the device is brought up.  Add the missing\ntest.\n\nDiscovered by XBOW, triaged by Baul Lee \u003cbaul.lee@xbow.com\u003e"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached only via local RTNETLINK on AF_NETLINK: RTM_NEWLINK creates a vxlan netdev, changelink with IFLA_VXLAN_AGEING arms age_timer, and RTM_DELLINK frees it; remote VXLAN encapsulation/packet receive is not involved.\nAC:L - The attacker fully controls a deterministic sequence on a never-up device: changelink calls mod_timer(jiffies) and dellink frees netdev while the timer stays queued because netif_close_many skips IFF_UP-less devices so vxlan_stop/timer_delete_sync never runs.\nPR:L - rtnetlink_rcv_msg requires CAP_NET_ADMIN for RTM_NEWLINK, RTM_SETLINK, and RTM_DELLINK; unprivileged local users obtain this capability inside a new user and network namespace (unshare -Urn), as stated in the fix commit.\nUI:N - No victim interaction is required; the attacker alone issues netlink create/changelink/delete operations on their own down vxlan interface without bringing the device up or requiring mounts or file access.\nS:C - Slab UAF corruption triggered from CAP_NET_ADMIN inside an unprivileged user/network namespace affects host kernel timer-list memory outside the namespace sandbox, crossing the container-to-host security boundary.\nC:H - KASAN reports slab-use-after-free with an 8-byte write through freed vxlan_dev-\u003eage_timer list pointers in __run_timers; UAF on kernel timer structures enables arbitrary kernel memory disclosure via slab heap reuse.\nI:H - expire_timers() writes to freed timer_list entry fields before loading the callback, providing controlled slab corruption; UAF on embedded vxlan_dev timers is exploitable for arbitrary kernel writes and privilege escalation.\nA:H - Confirmed KASAN slab-use-after-free in run_timer_softirq can kernel oops/panic; the dangling timer remains armed after rtnl_dellink and the sequence can be repeated for reliable denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-25T05:40:42.219Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/be44d79d14d7f9ae7c8ffb7272142005341b5123"
        },
        {
          "url": "https://git.kernel.org/stable/c/26c179d47403d2f919ee914cc02c31d896b59fee"
        },
        {
          "url": "https://git.kernel.org/stable/c/9dc561f0522c35bdd66e0646a748814a138ec4ca"
        },
        {
          "url": "https://git.kernel.org/stable/c/619dd29045e439d0b0f8c6d4fec1af447a050680"
        },
        {
          "url": "https://git.kernel.org/stable/c/6b095e99b9e67ea31f0c4b00260e010898253519"
        },
        {
          "url": "https://git.kernel.org/stable/c/46bb297ad77680e009244f067f27d51cf5b8c7cf"
        },
        {
          "url": "https://git.kernel.org/stable/c/6b4119af544996a545cf84b16f1dbce829ba0de8"
        },
        {
          "url": "https://git.kernel.org/stable/c/b37971686ec59fb027fa4910ba16805e68fddb97"
        }
      ],
      "title": "vxlan: do not arm the ageing timer on a device that is down",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74615",
    "datePublished": "2026-08-22T15:32:00.588Z",
    "dateReserved": "2026-08-15T05:44:03.920Z",
    "dateUpdated": "2026-08-25T05:40:42.219Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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