{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21637",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21637"
  ],
  "published": "2025-01-19T10:18:03Z",
  "summary": "sctp: sysctl: udp_port: avoid using current->nsproxy",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nsctp: sysctl: udp_port: avoid using current->nsproxy\n\nAs mentioned in a previous commit of this series, using the 'net'\nstructure via 'current' is not recommended for different reasons:\n\n- Inconsistency: getting info from the reader's/writer's netns vs only\n  from the opener's netns.\n\n- current->nsproxy can be NULL in some cases, resulting in an 'Oops'\n  (null-ptr-deref), e.g. when the current task is exiting, as spotted by\n  syzbot [1] using acct(2).\n\nThe 'net' structure can be obtained from the table->data using\ncontainer_of().\n\nNote that table->data could also be used directly, but that would\nincrease the size of this fix, while 'sctp.ctl_sock' still needs to be\nretrieved from 'net' structure.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2025-21637"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/0a0966312ac3eedd7f5f2a766ed4702df39a9a65"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/e919197fb8616331f5dc81e4c3cc3d12769cb725"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/55627918febdf9d71107a1e68d1528dc591c9a15"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/5b77d73f3be5102720fb685b9e6900e3500e1096"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c10377bbc1972d858eaf0ab366a311b39f8ef1b6"
    }
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  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T12:19:11Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.1,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - Despite living in net/sctp/, the vulnerable function is a procfs sysctl ->proc_handler reachable only through local file I/O on /proc/sys/net/sctp/udp_port and local syscalls (acct(2), write(2)); no received SCTP or UDP packet ever reaches it.\nAC:L - Both trigger paths are fully deterministic and entirely attacker-driven \u2014 either unshare/open/SCM_RIGHTS/write for the netns-confusion path, or acct(2) plus `umount -l` plus process exit for the NULL deref \u2014 with no race, no victim state, and no memory-layout dependency.\nPR:L - An unprivileged user can reach the flaw via `unshare -Urn`, since cap_capable() grants the owner of a child user namespace CAP_NET_ADMIN over it (security/commoncap.c:92), letting a process still in the init netns write through the child's sysctl fd and have the handler act on init_net; no real root is needed for that path.\nUI:N - The attacker performs every step from its own cooperating processes \u2014 namespace creation, fd passing, the write, or its own exit \u2014 with no action required from any other user or administrator.\nS:U - The flawed code and the affected resources are both kernel network-namespace state within the same kernel security authority; no hypervisor, IOMMU, or VM boundary is crossed.\nC:N - The NULL+offset dereference faults before returning any data, and the read side of the netns confusion only reports the caller's own netns value for a world-readable (0644) setting, so no protected information is disclosed.\nI:H - The netns confusion lets an unprivileged local user write init_net.sctp.udp_port and drive sctp_udp_sock_stop()/sctp_udp_sock_start() on the host namespace, fully controlling whether and on which port the host kernel decapsulates SCTP from UDP \u2014 an attacker-chosen modification of protected host network state and a bypass of SCTP packet filtering.\nA:H - The NULL-ptr-deref oops fires inside do_exit() while acct->lock is held, wedging the exiting task with a stuck mutex and pinned mount and panicking outright on panic_on_oops builds; separately, the cross-netns write destroys the host's SCTP UDP tunnel sockets, severing SCTP-over-UDP connectivity."
    }
  }
}