{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-39963",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-39963"
  ],
  "published": "2025-10-09T12:15:19Z",
  "summary": "io_uring: fix incorrect io_kiocb reference in io_link_skb",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring: fix incorrect io_kiocb reference in io_link_skb\n\nIn io_link_skb function, there is a bug where prev_notif is incorrectly\nassigned using 'nd' instead of 'prev_nd'. This causes the context\nvalidation check to compare the current notification with itself instead\nof comparing it with the previous notification.\n\nFix by using the correct prev_nd parameter when obtaining prev_notif.",
  "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-2025-39963"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a89c34babc2e5834aa0905278f26f4dbe4b26b76"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/50a98ce1ea694f1ff8e87bc2f8f84096d1736f6a"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/2c139a47eff8de24e3350dadb4c9d5e3426db826"
    }
  ],
  "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": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The vulnerability is reached by submitting `IORING_OP_SEND_ZC` SQEs on a local io_uring instance, requiring local process execution; the attacker is the sender, so no remote peer can drive the path.\nAC:L - A single unprivileged process deterministically sets up the condition by creating two rings/threads and issuing consecutive SEND_ZC requests on one shared TCP socket whose peer is not draining, and it controls both sides of the subsequent cross-ring `compl_reqs` race.\nPR:L - No capability check exists anywhere on the path \u2014 `io_uring_setup()`, `io_send_zc_prep()`, and `tcp_sendmsg_locked()` are all available to any unprivileged user with default `kernel.io_uring_disabled=0`.\nUI:N - The attacker performs the entire sequence \u2014 ring creation, socket setup, and both zerocopy sends \u2014 inside their own process with no victim action required.\nS:U - The corruption is confined to the kernel's own io_uring request cache and completion lists; no virtualization, IOMMU, or other security-authority boundary is crossed.\nC:H - Corrupting another ring's `compl_reqs` list makes the same `io_kiocb` reachable from two live operations and posts CQEs into a foreign ring's completion queue, yielding a use-after-free that can be groomed into an arbitrary kernel-memory read.\nI:H - `io_free_batch_list()` runs `io_put_file()`, `io_put_task()`, and `io_req_add_to_cache()` on the corrupted list, giving double-free of `req_cachep` objects and `struct file` refcount underflow \u2014 classic stepping stones to arbitrary write and local privilege escalation.\nA:H - Even without successful grooming, cross-context chaining reliably produces list corruption, leaked never-completed requests that hang task/ring teardown, and on 6.18-era kernels a `WARN_ON_ONCE` that panics under `panic_on_warn`."
    }
  }
}