{"cve":"CVE-2025-38470","nvd":{"published":"2025-07-28T12:15:28.760","modified":"2026-10-15T22:18:42.247","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: vlan: fix VLAN 0 refcount imbalance of toggling filtering during runtime\n\nAssuming the \"rx-vlan-filter\" feature is enabled on a net device, the\n8021q module will automatically add or remove VLAN 0 when the net device\nis put administratively up or down, respectively. There are a couple of\nproblems with the above scheme.\n\nThe first problem is a memory leak that can happen if the \"rx-vlan-filter\"\nfeature is disabled while the device is running:\n\n # ip link add bond1 up type bond mode 0\n # ethtool -K bond1 rx-vlan-filter off\n # ip link del dev bond1\n\nWhen the device is put administratively down the \"rx-vlan-filter\"\nfeature is disabled, so the 8021q module will not remove VLAN 0 and the\nmemory will be leaked [1].\n\nAnother problem that can happen is that the kernel can automatically\ndelete VLAN 0 when the device is put administratively down despite not\nadding it when the device was put administratively up since during that\ntime the \"rx-vlan-filter\" feature was disabled. null-ptr-unref or\nbug_on[2] will be triggered by unregister_vlan_dev() for refcount\nimbalance if toggling filtering during runtime:\n\n$ ip link add bond0 type bond mode 0\n$ ip link add link bond0 name vlan0 type vlan id 0 protocol 802.1q\n$ ethtool -K bond0 rx-vlan-filter off\n$ ifconfig bond0 up\n$ ethtool -K bond0 rx-vlan-filter on\n$ ifconfig bond0 down\n$ ip link del vlan0\n\nRoot cause is as below:\nstep1: add vlan0 for real_dev, such as bond, team.\nregister_vlan_dev\n    vlan_vid_add(real_dev,htons(ETH_P_8021Q),0) //refcnt=1\nstep2: disable vlan filter feature and enable real_dev\nstep3: change filter from 0 to 1\nvlan_device_event\n    vlan_filter_push_vids\n        ndo_vlan_rx_add_vid //No refcnt added to real_dev vlan0\nstep4: real_dev down\nvlan_device_event\n    vlan_vid_del(dev, htons(ETH_P_8021Q), 0); //refcnt=0\n        vlan_info_rcu_free //free vlan0\nstep5: delete vlan0\nunregister_vlan_dev\n    BUG_ON(!vlan_info); //vlan_info is null\n\nFix both problems by noting in the VLAN info whether VLAN 0 was\nautomatically added upon NETDEV_UP and based on that decide whether it\nshould be deleted upon NETDEV_DOWN, regardless of the state of the\n\"rx-vlan-filter\" feature.\n\n[1]\nunreferenced object 0xffff8880068e3100 (size 256):\n  comm \"ip\", pid 384, jiffies 4296130254\n  hex dump (first 32 bytes):\n    00 20 30 0d 80 88 ff ff 00 00 00 00 00 00 00 00  . 0.............\n    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................\n  backtrace (crc 81ce31fa):\n    __kmalloc_cache_noprof+0x2b5/0x340\n    vlan_vid_add+0x434/0x940\n    vlan_device_event.cold+0x75/0xa8\n    notifier_call_chain+0xca/0x150\n    __dev_notify_flags+0xe3/0x250\n    rtnl_configure_link+0x193/0x260\n    rtnl_newlink_create+0x383/0x8e0\n    __rtnl_newlink+0x22c/0xa40\n    rtnl_newlink+0x627/0xb00\n    rtnetlink_rcv_msg+0x6fb/0xb70\n    netlink_rcv_skb+0x11f/0x350\n    netlink_unicast+0x426/0x710\n    netlink_sendmsg+0x75a/0xc20\n    __sock_sendmsg+0xc1/0x150\n    ____sys_sendmsg+0x5aa/0x7b0\n    ___sys_sendmsg+0xfc/0x180\n\n[2]\nkernel BUG at net/8021q/vlan.c:99!\nOops: invalid opcode: 0000 [#1] SMP KASAN PTI\nCPU: 0 UID: 0 PID: 382 Comm: ip Not tainted 6.16.0-rc3 #61 PREEMPT(voluntary)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996),\nBIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014\nRIP: 0010:unregister_vlan_dev (net/8021q/vlan.c:99 (discriminator 1))\nRSP: 0018:ffff88810badf310 EFLAGS: 00010246\nRAX: 0000000000000000 RBX: ffff88810da84000 RCX: ffffffffb47ceb9a\nRDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88810e8b43c8\nRBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff6cefe80\nR10: ffffffffb677f407 R11: ffff88810badf3c0 R12: ffff88810e8b4000\nR13: 0000000000000000 R14: ffff88810642a5c0 R15: 000000000000017e\nFS:  00007f1ff68c20c0(0000) GS:ffff888163a24000(0000) knlGS:0000000000000000\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 00007f1ff5dad240 CR3: 0000000107e56000 CR4: 00000000000006f0\nCall Trace:\n <TASK\n---truncated---","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/047b61a24d7c866c502aeeea482892969a68f216","https://git.kernel.org/stable/c/35142b3816832889e50164d993018ea5810955ae","https://git.kernel.org/stable/c/579d4f9ca9a9a605184a9b162355f6ba131f678d","https://git.kernel.org/stable/c/8984bcbd1edf5bee5be06ad771d157333b790c33","https://git.kernel.org/stable/c/93715aa2d80e6c5cea1bb486321fc4585076928b"],"products":["debian:debian_linux","linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:05:46.678065081+00:00"},"epss":{"cve":"CVE-2025-38470","score":0.00192,"percentile":0.08767,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}