CVE-2026-43402 (GCVE-0-2026-43402)
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: kthread: consolidate kthread exit paths to prevent use-after-free Guillaume reported crashes via corrupted RCU callback function pointers during KUnit testing. The crash was traced back to the pidfs rhashtable conversion which replaced the 24-byte rb_node with an 8-byte rhash_head in struct pid, shrinking it from 160 to 144 bytes. struct kthread (without CONFIG_BLK_CGROUP) is also 144 bytes. With CONFIG_SLAB_MERGE_DEFAULT and SLAB_HWCACHE_ALIGN both round up to 192 bytes and share the same slab cache. struct pid.rcu.func and struct kthread.affinity_node both sit at offset 0x78. When a kthread exits via make_task_dead() it bypasses kthread_exit() and misses the affinity_node cleanup. free_kthread_struct() frees the memory while the node is still linked into the global kthread_affinity_list. A subsequent list_del() by another kthread writes through dangling list pointers into the freed and reused memory, corrupting the pid's rcu.func pointer. Instead of patching free_kthread_struct() to handle the missed cleanup, consolidate all kthread exit paths. Turn kthread_exit() into a macro that calls do_exit() and add kthread_do_exit() which is called from do_exit() for any task with PF_KTHREAD set. This guarantees that kthread-specific cleanup always happens regardless of the exit path - make_task_dead(), direct do_exit(), or kthread_exit(). Replace __to_kthread() with a new tsk_is_kthread() accessor in the public header. Export do_exit() since module code using the kthread_exit() macro now needs it directly.
References
Impacted products
Vendor Product Version
Linux Linux Version: 4d13f4304fa43471bfea101658a11feec7b28ac0
Version: 4d13f4304fa43471bfea101658a11feec7b28ac0
Version: 4d13f4304fa43471bfea101658a11feec7b28ac0
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/linux/kthread.h",
            "kernel/exit.c",
            "kernel/kthread.c"
          ],
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          "vendor": "Linux",
          "versions": [
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              "versionType": "git"
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            "kernel/exit.c",
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          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.14"
            },
            {
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.19",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.19.*",
              "status": "unaffected",
              "version": "6.19.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.0",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.19",
                  "versionStartIncluding": "6.14",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "6.19.9",
                  "versionStartIncluding": "6.14",
                  "vulnerable": true
                },
                {
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                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nkthread: consolidate kthread exit paths to prevent use-after-free\n\nGuillaume reported crashes via corrupted RCU callback function pointers\nduring KUnit testing. The crash was traced back to the pidfs rhashtable\nconversion which replaced the 24-byte rb_node with an 8-byte rhash_head\nin struct pid, shrinking it from 160 to 144 bytes.\n\nstruct kthread (without CONFIG_BLK_CGROUP) is also 144 bytes. With\nCONFIG_SLAB_MERGE_DEFAULT and SLAB_HWCACHE_ALIGN both round up to\n192 bytes and share the same slab cache. struct pid.rcu.func and\nstruct kthread.affinity_node both sit at offset 0x78.\n\nWhen a kthread exits via make_task_dead() it bypasses kthread_exit() and\nmisses the affinity_node cleanup. free_kthread_struct() frees the memory\nwhile the node is still linked into the global kthread_affinity_list. A\nsubsequent list_del() by another kthread writes through dangling list\npointers into the freed and reused memory, corrupting the pid\u0027s\nrcu.func pointer.\n\nInstead of patching free_kthread_struct() to handle the missed cleanup,\nconsolidate all kthread exit paths. Turn kthread_exit() into a macro\nthat calls do_exit() and add kthread_do_exit() which is called from\ndo_exit() for any task with PF_KTHREAD set. This guarantees that\nkthread-specific cleanup always happens regardless of the exit path -\nmake_task_dead(), direct do_exit(), or kthread_exit().\n\nReplace __to_kthread() with a new tsk_is_kthread() accessor in the\npublic header. Export do_exit() since module code using the\nkthread_exit() macro now needs it directly."
        }
      ],
      "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 - In the most severe reasonable deployment, network-facing in-kernel services such as ksmbd create kthreads and process unauthenticated remote traffic in those kthreads. The vulnerable kthread lifecycle and exit cleanup can therefore be reached from a remote network path.\nAC:L - The bug is a deterministic cleanup omission once an affected kthread exits through a bypass path such as make_task_dead/do_exit, and the resulting dangling list entry can be exercised by normal kthread churn. There is no attacker-uncontrolled race required for the UAF mechanism itself.\nPR:N - For network-facing kthread users such as ksmbd connection handlers, an unauthenticated remote peer can drive pre-authentication packet handling and connection-thread creation. No local account or kernel capability is required in that scenario.\nUI:N - Exploitation does not require a victim user to open a file, mount a filesystem, or perform another interactive action. The attacker can send traffic or otherwise drive the reachable service path directly.\nS:U - The corruption occurs within the Linux kernel and impacts kernel-managed memory and control flow. It does not inherently cross a separate security authority such as a VM-to-host or IOMMU boundary.\nC:H - This is a use-after-free of a freed struct kthread left linked into a global list, with later list operations writing into reused slab memory such as struct pid. Kernel UAF memory corruption is treated as capable of yielding high confidentiality impact through read/info-disclosure primitives.\nI:H - The stale list entry causes writes through dangling list pointers into a reused object, including corruption of sensitive fields such as an RCU callback pointer. Such kernel UAF corruption is defensibly exploitable for arbitrary write or control-flow hijack.\nA:H - The observed failure mode is corrupted RCU callback function pointers and kernel crashes. Even without full exploitation, repeated triggering can oops or panic the kernel, causing high availability impact."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:27:46.142Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4729c7b00a347fd37d0cbc265b85f2884c3e06b6"
        },
        {
          "url": "https://git.kernel.org/stable/c/5a591d7a5e48d30100943940a30a6ab41b15c672"
        },
        {
          "url": "https://git.kernel.org/stable/c/28aaa9c39945b7925a1cc1d513c8f21ed38f5e4f"
        }
      ],
      "title": "kthread: consolidate kthread exit paths to prevent use-after-free",
      "x_generator": {
        "engine": "bippy-1.2.0"
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    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-43402",
    "datePublished": "2026-05-08T14:21:43.550Z",
    "dateReserved": "2026-05-01T14:12:56.007Z",
    "dateUpdated": "2026-08-05T12:27:46.142Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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