CVE-2026-43376 (GCVE-0-2026-43376)
Vulnerability from cvelistv5
Published
2026-05-08 14:21
Modified
2026-08-05 12:27
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free by using call_rcu() for oplock_info ksmbd currently frees oplock_info immediately using kfree(), even though it is accessed under RCU read-side critical sections in places like opinfo_get() and proc_show_files(). Since there is no RCU grace period delay between nullifying the pointer and freeing the memory, a reader can still access oplock_info structure after it has been freed. This can leads to a use-after-free especially in opinfo_get() where atomic_inc_not_zero() is called on already freed memory. Fix this by switching to deferred freeing using call_rcu().
References
Impacted products
Vendor Product Version
Linux Linux Version: 296cb5457cc6f4a754c4ae29855f8a253d52bcc6
Version: d54ab1520d43e95f9b2e22d7a05fc9614192e5a5
Version: 18b4fac5ef17f77fed9417d22210ceafd6525fc7
Version: 18b4fac5ef17f77fed9417d22210ceafd6525fc7
Version: 18b4fac5ef17f77fed9417d22210ceafd6525fc7
Version: d73686367ad68534257cd88a36ca3c52cb8b81d8
Version: 6.6.88   ≤
Version: 6.12.25   ≤
Version: 6.14.4   ≤
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/oplock.c",
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              "status": "unaffected",
              "version": "7.0",
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      ],
      "cpeApplicability": [
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          "nodes": [
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              "cpeMatch": [
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free by using call_rcu() for oplock_info\n\nksmbd currently frees oplock_info immediately using kfree(), even\nthough it is accessed under RCU read-side critical sections in places\nlike opinfo_get() and proc_show_files().\n\nSince there is no RCU grace period delay between nullifying the pointer\nand freeing the memory, a reader can still access oplock_info\nstructure after it has been freed. This can leads to a use-after-free\nespecially in opinfo_get() where atomic_inc_not_zero() is called on\nalready freed memory.\n\nFix this by switching to deferred freeing using call_rcu()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - ksmbd is the in-kernel SMB server reachable over TCP/445, and the vulnerable oplock_info lifetime is exercised by remote SMB2 create/close/oplock and lease operations.\nAC:L - The attacker can create oplocks/leases and drive concurrent requests over SMB connections, so the race is attacker-controlled rather than dependent on an external victim condition.\nPR:N - The path is post-session/tree-connect, but ksmbd supports guest/public shares; in the highest reasonable oplocks-enabled guest-share deployment, no prior credentials are needed.\nUI:N - No victim user action is required once the SMB service and share are available; the attacker sends network protocol requests directly.\nS:U - The vulnerable component and impacted resources are the same kernel/host security authority, with no VM, hypervisor, or other scope boundary crossing.\nC:H - This is a kernel heap use-after-free on oplock_info, including stale pointer dereferences after freed memory can be reallocated, which can reasonably enable high-impact kernel information disclosure.\nI:H - The stale atomic_inc_not_zero and later field accesses can corrupt a reallocated kernel object, making arbitrary kernel memory modification or code execution defensible.\nA:H - The UAF can directly trigger kernel memory corruption, oops, panic, or hang, causing high availability impact."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:27:35.730Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/302fef75512b2c8329a3f5efab1ae7ba2562387a"
        },
        {
          "url": "https://git.kernel.org/stable/c/08aa9f3c8cf4d0bee44df540dfe34e8d64069f2c"
        },
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          "url": "https://git.kernel.org/stable/c/1d6abf145615dbfe267ce3b0a271f95e3780e18e"
        },
        {
          "url": "https://git.kernel.org/stable/c/ce8507ee82c888126d8e7565e27c016308d24cde"
        },
        {
          "url": "https://git.kernel.org/stable/c/1dfd062caa165ec9d7ee0823087930f3ab8a6294"
        }
      ],
      "title": "ksmbd: fix use-after-free by using call_rcu() for oplock_info",
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        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-43376",
    "datePublished": "2026-05-08T14:21:25.854Z",
    "dateReserved": "2026-05-01T14:12:56.006Z",
    "dateUpdated": "2026-08-05T12:27:35.730Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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