{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21763",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21763"
  ],
  "published": "2025-02-27T02:18:18Z",
  "summary": "neighbour: use RCU protection in __neigh_notify()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nneighbour: use RCU protection in __neigh_notify()\n\n__neigh_notify() can be called without RTNL or RCU protection.\n\nUse RCU protection to avoid potential UAF.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-21763"
    },
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      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The decisive side of the race \u2014 `dev_net_set()` during netdevice namespace migration or `default_device_exit_batch()` on netns teardown, followed by freeing the `struct net` \u2014 is driven only by local syscalls (`unshare(CLONE_NEWNET|CLONE_NEWUSER)`, RTM_NEWLINK/RTM_SETLINK). A purely remote or adjacent peer can generate ARP/NDISC traffic to reach `__neigh_notify()` but cannot cause the namespace pointer to go stale.\nAC:L - The attacker controls both sides: they spin a loop creating/destroying network namespaces with veth devices while concurrently driving neighbour add/update/GC notifications on other CPUs, so the race is created rather than waited for. Per race-condition guidance, attacker-created races are Low even though the window between the `dev_net()` load and the `net->rtnl` dereference is narrow.\nPR:L - `unshare -Urn` grants namespace-relative CAP_NET_ADMIN (`ns_capable(net->user_ns, CAP_NET_ADMIN)`), letting an ordinary unprivileged user create netns, create and move veth pairs, and trigger the teardown path; no real root is needed. Neighbour-table activity that reaches `__neigh_notify()` is likewise available to any unprivileged process.\nUI:N - The attacker triggers both the namespace teardown and the neighbour notifications entirely from their own processes. No victim action, mount, or file open is involved.\nS:U - The use-after-free and its consequences are confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed. This is standard in-kernel corruption leading to local privilege escalation.\nC:H - The freed `struct net` is a reclaimable `net_cachep` slab object, and `net->rtnl` is subsequently consumed as a `struct sock *` by `netlink_set_err()`/`nlmsg_notify()`, which read `sk->sk_protocol` and `sock_net(sk)` and walk netlink tables from it. Heap-spraying the freed object turns this into an attacker-directed kernel read primitive.\nI:H - With the freed `struct net` reclaimed under attacker control, `netlink_set_err()` writes through the forged `sk` pointer (`sk->sk_err = err`, list/waitqueue manipulation), giving a controlled kernel write usable for control-flow hijacking. Per guidance, use-after-free is scored High for integrity.\nA:H - Even without successful reclaim, dereferencing the freed `struct net` and the dangling `net->rtnl` socket causes a kernel oops or panic in `nlmsg_notify()`/`netlink_set_err()`. The trigger loop can be repeated indefinitely by an unprivileged user."
    }
  }
}