{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-39698",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-39698"
  ],
  "published": "2025-09-05T17:22:05Z",
  "summary": "io_uring/futex: ensure io_futex_wait() cleans up properly on failure",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/futex: ensure io_futex_wait() cleans up properly on failure\n\nThe io_futex_data is allocated upfront and assigned to the io_kiocb\nasync_data field, but the request isn't marked with REQ_F_ASYNC_DATA\nat that point. Those two should always go together, as the flag tells\nio_uring whether the field is valid or not.\n\nAdditionally, on failure cleanup, the futex handler frees the data but\ndoes not clear ->async_data. Clear the data and the flag in the error\npath as well.\n\nThanks to Trend Micro Zero Day Initiative and particularly ReDress for\nreporting this.",
  "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-2025-39698"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/d9f93172820a53ab42c4b0e5e65291f4f9d00ad2"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/d34c04152df517c59979b4bf2a47f491e06d3256"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/508c1314b342b78591f51c4b5dadee31a88335df"
    }
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    "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 purely through the io_uring interface \u2014 `io_uring_setup(2)` plus an SQE with `IORING_OP_FUTEX_WAIT` \u2014 which requires local code execution on the system. There is no remote or adjacent-network path into `io_futex_wait()`.\nAC:L - The failure path is hit deterministically by submitting a FUTEX_WAIT SQE whose `futex_val` does not match `*uaddr` (returns -EWOULDBLOCK) or with an unmapped `uaddr` (-EFAULT); no race or timing window is involved. The attacker also fully controls request recycling and heap grooming, since the freed `io_futex_data` lands in a general-purpose kmalloc cache and the sequence can be repeated arbitrarily.\nPR:L - `sysctl_io_uring_disabled` defaults to 0, so any unprivileged user can create a ring, and `IORING_OP_FUTEX_WAIT` requires no file, no capability, and no privileged setup (`io_futex_prep` only validates futex2 flags). No root or namespace trickery is needed.\nUI:N - The attacker submits all SQEs from their own process and drives the entire sequence \u2014 failing futex wait, request recycling, then POLL_ADD \u2014 with no action by any other user. No victim process or administrator involvement is required.\nS:U - The use-after-free occurs in kernel heap memory managed by the same kernel security authority as the attacking process. Exploitation yields kernel privilege escalation rather than crossing a VM, IOMMU, or other separate security boundary.\nC:H - The stale `req->async_data` is dereferenced as a `struct io_poll *` in `__io_queue_proc()` (`(*poll_ptr)->head`), reading freed slab memory that the attacker can reclaim and shape, giving a controllable kernel-memory read/type-confusion primitive. Consistent with the guidance, a use-after-free of an attacker-reclaimable heap object is scored as High confidentiality impact.\nI:H - The dangling pointer is stored in a recycled `io_kiocb` and later treated as a live `struct io_poll`, so poll teardown (`io_poll_remove_entry()`'s `list_del_init(&poll->wait.entry)` / `poll->head = NULL`) and `__io_futex_cancel()`'s unguarded `futex_unqueue(&ifd->q)` operate on attacker-reclaimed memory. This is the classic io_uring UAF/type-confusion shape that is leveraged into arbitrary write and local privilege escalation, which is why ZDI reported it.\nA:H - Dereferencing the freed `io_futex_data` as an `io_poll` reliably produces slab corruption, KASAN splats, and kernel oopses/panics even without a successful exploit. Any unprivileged user can repeat the trigger at will to crash the machine."
    }
  }
}