{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21762",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21762"
  ],
  "published": "2025-02-27T02:18:18Z",
  "summary": "arp: use RCU protection in arp_xmit()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\narp: use RCU protection in arp_xmit()\n\narp_xmit() 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:N/AC:H/PR:N/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-2025-21762"
    },
    {
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      "cvss_v3_score": 8.1,
      "cvss_v3_severity": "High",
      "scenario": "AV:N - The unprotected `arp_xmit()` calls are driven by the neighbour-resolution path (`neigh_timer_handler` \u2192 `neigh_probe` \u2192 `arp_solicit`), which a remote off-link attacker triggers at will by sending traffic to a Linux router/gateway that must resolve on-link next hops, as well as by ARP frames processed in `arp_process()`/bridge neigh-suppression. The vulnerable code is bound to the network stack and reachable from remotely originated packets, so Network is the correct and higher-severity classification.\nAC:H - The attacker fully controls and can sustain the ARP-transmit side of the race, but the other side \u2014 a `struct net` being freed via `cleanup_net()` or a device migrating namespaces \u2014 is background system activity the network attacker cannot command. Because that condition lies outside attacker control, complexity is High.\nPR:N - There is no capability check, credential check, or authentication gate anywhere on the path from packet receipt/neighbour resolution to `arp_xmit()`; ARP solicitation and reply generation happen unconditionally in softirq context. An entirely unauthenticated attacker reaches the vulnerable code.\nUI:N - The attacker's own packets cause the kernel to emit ARP and execute the vulnerable code; no victim must mount a filesystem, open a file, or take any other action.\nS:U - The use-after-free of `struct net` and the resulting corruption stay entirely within the kernel's own security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - A use-after-free of `struct net` lets `nf_hook()` read `net->nf.hooks_arp[]` and every ARP-family hook read `state->net` out of freed, potentially reallocated slab memory. Per kernel guidance a UAF gives the attacker control over the freed object's contents and thus an arbitrary kernel-memory read primitive.\nI:H - The stale `net` yields a `hook_head` pointer from freed memory, and `nf_hook_slow()` then performs an indirect call through `e->hooks[s].hook` \u2014 a direct function-pointer hijack primitive if the netns slab is reallocated with sprayed data. Hooks also write through `state->net`, corrupting reused kernel objects.\nA:H - Dereferencing a freed `struct net` and calling through a garbage `nf_hook_entries` reliably oopses or panics the kernel, and is a KASAN-reportable memory-safety violation that panics on hardened configurations. Any such kernel crash is scored High."
    }
  }
}