{
  "cveId": "CVE-2026-43121",
  "url": "https://patchblox.com/security/cve/CVE-2026-43121",
  "summary": "CVE-2026-43121 is fixed in 23 products on 1 platform, first by ALAS2023-2026-1702, released May 11, 2026. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  io_uring/zcrx: fix user_ref race between scrub a...",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  io_uring/zcrx: fix user_ref race between scrub and refill paths  The io_zcrx_put_niov_uref() function uses a non-atomic check-then-decrement pattern (atomic_read followed by separate atomic_dec) to manipulate user_refs. This is serialized against other callers by rq_lock, but io_zcrx_scrub() modifies the same counter with atomic_xchg() WITHOUT holding rq_lock.  On SMP systems, the following race exists:    CPU0 (refill, holds rq_lock)          CPU1 (scrub, no rq_lock)   put_niov_uref:     atomic_read(uref) - 1     // window opens                                         atomic_xchg(uref, 0) - 1                                         return_niov_freelist(niov) [PUSH #1]     // window closes     atomic_dec(uref) - wraps to -1     returns true     return_niov(niov)     return_niov_freelist(niov)           [PUSH #2: DOUBLE-FREE]  The same niov is pushed to the freelist twice, causing free_count to exceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds write (a u32 value) past the kvmalloc\u0027d freelist array into the adjacent slab object.  Fix this by replacing the non-atomic read-then-dec in io_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically tests and decrements user_refs. This makes the operation safe against concurrent atomic_xchg from scrub without requiring scrub to acquire rq_lock.  [pavel: removed a warning and a comment]",
  "published": "2026-05-06T12:16:28Z",
  "severity": "medium",
  "cvss": 4.7,
  "cvssVector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
  "epss": 0.00111,
  "epssPercentile": 0.01357,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "bpftool6.18",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
      "platform": "linux",
      "product": "bpftool6.18-debuginfo",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
      "platform": "linux",
      "product": "kernel-livepatch-6.18.16-18.222",
      "release": "amzn 2023",
      "fixedVersion": "1:1.0-0.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "product": "kernel6.18",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "product": "kernel6.18-debuginfo",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
      "platform": "linux",
      "product": "kernel6.18-debuginfo-common-aarch64",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "product": "kernel6.18-debuginfo-common-x86_64",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "release": "amzn 2023",
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
      "platform": "linux",
      "product": "kernel6.18-headers",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "release": "amzn 2023",
      "fixedVersion": "1:6.18.16-18.222.amzn2023",
      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "release": "amzn 2023",
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
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      "fix": "ALAS2023-2026-1702",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "6.19.6-1",
      "fix": "DEBIAN-CVE-2026-43121",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-43121",
      "released": "2026-05-15T16:01:09Z"
    },
    {
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      "release": "amzn 2023",
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      "fix": "ALAS2023-2026-1702",
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      "released": "2026-05-11T09:00:00Z"
    },
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      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
      "released": "2026-05-11T09:00:00Z"
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      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1702",
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      "released": "2026-05-11T09:00:00Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T19:12:23Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}