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EUVD-2026-344428

European Vulnerability Database identifier assigned by ENISA

Reserved

2026-10-02 07:56

Assigner

ENISA

Alias of

a CVE record, shown under related vulnerabilities. This identifier carries no description, severity or references of its own: they belong to that CVE.

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{
  "assigner": "ENISA",
  "date_reserved": "2026-10-02T07:56:12.971392+00:00",
  "id": "EUVD-2026-344428"
}

CVE-2021-47222 (GCVE-0-2021-47222)

Vulnerability from cvelistv5 – Published: 2024-05-21 14:19 – Updated: 2026-08-05 08:46

Title

net: bridge: fix vlan tunnel dst refcnt when egressing

Summary

In the Linux kernel, the following vulnerability has been resolved: net: bridge: fix vlan tunnel dst refcnt when egressing The egress tunnel code uses dst_clone() and directly sets the result which is wrong because the entry might have 0 refcnt or be already deleted, causing number of problems. It also triggers the WARN_ON() in dst_hold()[1] when a refcnt couldn't be taken. Fix it by using dst_hold_safe() and checking if a reference was actually taken before setting the dst. [1] dmesg WARN_ON log and following refcnt errors WARNING: CPU: 5 PID: 38 at include/net/dst.h:230 br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge] Modules linked in: 8021q garp mrp bridge stp llc bonding ipv6 virtio_net CPU: 5 PID: 38 Comm: ksoftirqd/5 Kdump: loaded Tainted: G W 5.13.0-rc3+ #360 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014 RIP: 0010:br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge] Code: e8 85 bc 01 e1 45 84 f6 74 90 45 31 f6 85 db 48 c7 c7 a0 02 19 a0 41 0f 94 c6 31 c9 31 d2 44 89 f6 e8 64 bc 01 e1 85 db 75 02 <0f> 0b 31 c9 31 d2 44 89 f6 48 c7 c7 70 02 19 a0 e8 4b bc 01 e1 49 RSP: 0018:ffff8881003d39e8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa01902a0 RBP: ffff8881040c6700 R08: 0000000000000000 R09: 0000000000000001 R10: 2ce93d0054fe0d00 R11: 54fe0d00000e0000 R12: ffff888109515000 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000401 FS: 0000000000000000(0000) GS:ffff88822bf40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f42ba70f030 CR3: 0000000109926000 CR4: 00000000000006e0 Call Trace: br_handle_vlan+0xbc/0xca [bridge] __br_forward+0x23/0x164 [bridge] deliver_clone+0x41/0x48 [bridge] br_handle_frame_finish+0x36f/0x3aa [bridge] ? skb_dst+0x2e/0x38 [bridge] ? br_handle_ingress_vlan_tunnel+0x3e/0x1c8 [bridge] ? br_handle_frame_finish+0x3aa/0x3aa [bridge] br_handle_frame+0x2c3/0x377 [bridge] ? __skb_pull+0x33/0x51 ? vlan_do_receive+0x4f/0x36a ? br_handle_frame_finish+0x3aa/0x3aa [bridge] __netif_receive_skb_core+0x539/0x7c6 ? __list_del_entry_valid+0x16e/0x1c2 __netif_receive_skb_list_core+0x6d/0xd6 netif_receive_skb_list_internal+0x1d9/0x1fa gro_normal_list+0x22/0x3e dev_gro_receive+0x55b/0x600 ? detach_buf_split+0x58/0x140 napi_gro_receive+0x94/0x12e virtnet_poll+0x15d/0x315 [virtio_net] __napi_poll+0x2c/0x1c9 net_rx_action+0xe6/0x1fb __do_softirq+0x115/0x2d8 run_ksoftirqd+0x18/0x20 smpboot_thread_fn+0x183/0x19c ? smpboot_unregister_percpu_thread+0x66/0x66 kthread+0x10a/0x10f ? kthread_mod_delayed_work+0xb6/0xb6 ret_from_fork+0x22/0x30 ---[ end trace 49f61b07f775fd2b ]--- dst_release: dst:00000000c02d677a refcnt:-1 dst_release underflow

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2024-09-10 15:40 UTC

Assigner

Linux mitre root Scorecard

References

6 references

URL	Tags
https://git.kernel.org/stable/c/42020f7f37a90d24b…
https://git.kernel.org/stable/c/84fc1c944e45ab317…
https://git.kernel.org/stable/c/79855be6445b6592b…
https://git.kernel.org/stable/c/fc7fdd8c5c2ad2fe3…
https://git.kernel.org/stable/c/25053a8404ba17ca4…
https://git.kernel.org/stable/c/cfc579f9d89af4ada…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 11538d039ac6efcf4f1a6c536e1b87cd3668a9fd , < 42020f7f37a90d24b9551f5f7eba3f7c7c102968 (git) Affected: 11538d039ac6efcf4f1a6c536e1b87cd3668a9fd , < 84fc1c944e45ab317e2e70a0e7f76fa2a5e43b6e (git) Affected: 11538d039ac6efcf4f1a6c536e1b87cd3668a9fd , < 79855be6445b6592bddb7bd7167083ec8cdbd73f (git) Affected: 11538d039ac6efcf4f1a6c536e1b87cd3668a9fd , < fc7fdd8c5c2ad2fe3e297698be9d4dbe4a4e0579 (git) Affected: 11538d039ac6efcf4f1a6c536e1b87cd3668a9fd , < 25053a8404ba17ca48f5553d487afc1882e9f56c (git) Affected: 11538d039ac6efcf4f1a6c536e1b87cd3668a9fd , < cfc579f9d89af4ada58c69b03bcaa4887840f3b3 (git)
Linux	Linux	Affected: 4.11 Unaffected: 0 , < 4.11 (semver) Unaffected: 4.14.238 , ≤ 4.14.* (semver) Unaffected: 4.19.196 , ≤ 4.19.* (semver) Unaffected: 5.4.128 , ≤ 5.4.* (semver) Unaffected: 5.10.46 , ≤ 5.10.* (semver) Unaffected: 5.12.13 , ≤ 5.12.* (semver) Unaffected: 5.13 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

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      "descriptions": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: fix vlan tunnel dst refcnt when egressing\n\nThe egress tunnel code uses dst_clone() and directly sets the result\nwhich is wrong because the entry might have 0 refcnt or be already deleted,\ncausing number of problems. It also triggers the WARN_ON() in dst_hold()[1]\nwhen a refcnt couldn\u0027t be taken. Fix it by using dst_hold_safe() and\nchecking if a reference was actually taken before setting the dst.\n\n[1] dmesg WARN_ON log and following refcnt errors\n WARNING: CPU: 5 PID: 38 at include/net/dst.h:230 br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge]\n Modules linked in: 8021q garp mrp bridge stp llc bonding ipv6 virtio_net\n CPU: 5 PID: 38 Comm: ksoftirqd/5 Kdump: loaded Tainted: G        W         5.13.0-rc3+ #360\n Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014\n RIP: 0010:br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge]\n Code: e8 85 bc 01 e1 45 84 f6 74 90 45 31 f6 85 db 48 c7 c7 a0 02 19 a0 41 0f 94 c6 31 c9 31 d2 44 89 f6 e8 64 bc 01 e1 85 db 75 02 \u003c0f\u003e 0b 31 c9 31 d2 44 89 f6 48 c7 c7 70 02 19 a0 e8 4b bc 01 e1 49\n RSP: 0018:ffff8881003d39e8 EFLAGS: 00010246\n RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000\n RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa01902a0\n RBP: ffff8881040c6700 R08: 0000000000000000 R09: 0000000000000001\n R10: 2ce93d0054fe0d00 R11: 54fe0d00000e0000 R12: ffff888109515000\n R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000401\n FS:  0000000000000000(0000) GS:ffff88822bf40000(0000) knlGS:0000000000000000\n CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 00007f42ba70f030 CR3: 0000000109926000 CR4: 00000000000006e0\n Call Trace:\n  br_handle_vlan+0xbc/0xca [bridge]\n  __br_forward+0x23/0x164 [bridge]\n  deliver_clone+0x41/0x48 [bridge]\n  br_handle_frame_finish+0x36f/0x3aa [bridge]\n  ? skb_dst+0x2e/0x38 [bridge]\n  ? br_handle_ingress_vlan_tunnel+0x3e/0x1c8 [bridge]\n  ? br_handle_frame_finish+0x3aa/0x3aa [bridge]\n  br_handle_frame+0x2c3/0x377 [bridge]\n  ? __skb_pull+0x33/0x51\n  ? vlan_do_receive+0x4f/0x36a\n  ? br_handle_frame_finish+0x3aa/0x3aa [bridge]\n  __netif_receive_skb_core+0x539/0x7c6\n  ? __list_del_entry_valid+0x16e/0x1c2\n  __netif_receive_skb_list_core+0x6d/0xd6\n  netif_receive_skb_list_internal+0x1d9/0x1fa\n  gro_normal_list+0x22/0x3e\n  dev_gro_receive+0x55b/0x600\n  ? detach_buf_split+0x58/0x140\n  napi_gro_receive+0x94/0x12e\n  virtnet_poll+0x15d/0x315 [virtio_net]\n  __napi_poll+0x2c/0x1c9\n  net_rx_action+0xe6/0x1fb\n  __do_softirq+0x115/0x2d8\n  run_ksoftirqd+0x18/0x20\n  smpboot_thread_fn+0x183/0x19c\n  ? smpboot_unregister_percpu_thread+0x66/0x66\n  kthread+0x10a/0x10f\n  ? kthread_mod_delayed_work+0xb6/0xb6\n  ret_from_fork+0x22/0x30\n ---[ end trace 49f61b07f775fd2b ]---\n dst_release: dst:00000000c02d677a refcnt:-1\n dst_release underflow"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is a race between bridge VLAN-tunnel deletion (rtnetlink RTM_SETLINK/DELLINK under RTNL) and the softirq egress path in br_handle_egress_vlan_tunnel(); a remote peer can only send frames and cannot drop tunnel_dst, so both sides must be driven locally via netlink.\nAC:L - An attacker who owns the netns controls both racing sides\u2014flooding frames through a BR_VLAN_TUNNEL port while concurrently deleting vlan tunnel info\u2014so the race is freely repeatable with no attacker-uncontrollable precondition.\nPR:L - Bridge creation, VLAN filtering, BR_VLAN_TUNNEL, and tunnel-id add/delete need only CAP_NET_ADMIN in the owning user/net namespace, which an unprivileged user obtains with unshare -Urn; real init-ns root is not required.\nUI:N - The attacker performs namespace setup, bridge/VLAN-tunnel configuration, traffic generation, and tunnel deletion entirely themselves; no victim interaction is required.\nS:U - The resulting metadata_dst use-after-free and refcnt underflow corrupt kernel heap within the same kernel security authority, with no VM/IOMMU/sandbox boundary crossed.\nC:H - dst_clone() still returns the dst after a failed hold, leaving the skb with a dangling metadata_dst that is freed via RCU; reclaiming that slab yields an arbitrary kernel-read primitive, so confidentiality impact is High.\nI:H - The dangling dst is later used for tunnel metadata on egress and released via dst_release, so an attacker-controlled reallocation provides write/corruption primitives suitable for control-flow hijack; integrity impact is High.\nA:H - The failed hold triggers WARN_ON in dst_hold(), dst_release underflow, and a softirq use-after-free that reliably oopses/panics the kernel and can be retriggered at will."
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      "title": "net: bridge: fix vlan tunnel dst refcnt when egressing",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2021-47222",
    "datePublished": "2024-05-21T14:19:28.214Z",
    "dateReserved": "2024-04-10T18:59:19.529Z",
    "dateUpdated": "2026-08-05T08:46:47.766Z",
    "state": "PUBLISHED"
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}

Sightings

Author	Source	Type	Date	Other

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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EUVD-2026-344428

CVE-2021-47222 (GCVE-0-2021-47222)

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Nomenclature

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