{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21759",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21759"
  ],
  "published": "2025-02-27T02:18:18Z",
  "summary": "ipv6: mcast: extend RCU protection in igmp6_send()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: mcast: extend RCU protection in igmp6_send()\n\nigmp6_send() can be called without RTNL or RCU being held.\n\nExtend RCU protection so that we can safely fetch the net pointer\nand avoid a potential UAF.\n\nNote that we no longer can use sock_alloc_send_skb() because\nipv6.igmp_sk uses GFP_KERNEL allocations which can sleep.\n\nInstead use alloc_skb() and charge the net->ipv6.igmp_sk\nsocket under RCU protection.",
  "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-2025-21759"
    },
    {
      "type": "FIX",
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      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - Although igmp6_send() can be scheduled by adjacent MLD Query packets, the freeing side of the race requires network-namespace dismantle or a netdev netns move, which is driven by local syscalls (unshare/setns, RTM_NEWLINK with IFLA_NET_NS_FD, process exit). A local unprivileged user controls both sides of the race entirely, making local access the reliable exploitation vector.\nAC:L - The attacker drives both halves: they schedule igmp6_send() at will (multicast join/leave, link up/down, or timed MLD reports) and trigger the free by destroying their own netns or moving the device out of it, and can retry the race indefinitely while heap-grooming the freed struct net/struct sock.\nPR:L - Only an unprivileged local account is needed \u2014 the CAP_NET_ADMIN checks on the netns-move path are ns_capable() against the target netns user_ns, which is satisfied inside a user namespace created with unshare -Urn, and IPv6 multicast joins require no privilege at all.\nUI:N - The entire sequence \u2014 namespace setup, multicast group joins, and namespace teardown \u2014 is performed by the attacker's own processes with no action from any other user.\nS:U - The corrupted objects (struct net, struct sock) and the resulting code execution are all within the kernel's own security authority; no hypervisor, IOMMU, or other security boundary is crossed.\nC:H - The use-after-free reads sk->sk_sndbuf, sk->sk_allocation, sk->sk_socket, net->mib pointers and net->nf.hooks_ipv6[] from freed-and-reallocated memory, giving an attacker who sprays the freed slab a controllable pointer-dereference primitive that can be turned into arbitrary kernel memory disclosure.\nI:H - skb_set_owner_w() performs refcount_add() into the freed socket and NF_HOOK() calls a function pointer fetched from the freed struct net's netfilter hook array, yielding both a write primitive and control-flow hijack suitable for full privilege escalation.\nA:H - Dereferencing a freed struct net and its igmp_sk reliably produces a kernel oops/panic (slab-use-after-free, invalid pointer dereference in the netfilter or socket accounting path), and the race can be repeated to crash the machine."
    }
  }
}