CVE-2026-63802 (GCVE-0-2026-63802)
Vulnerability from cvelistv5
Published
2026-07-19 12:02
Modified
2026-08-17 04:51
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: fix UAF in __blkcg_rstat_flush() When multiple blkgs in the same blkcg are released concurrently, a use-after-free can occur. The race happens when one blkg's __blkcg_rstat_flush() removes another blkg's iostat entries via llist_del_all(). The second blkg sees an empty list and proceeds to free itself while the first is still iterating over its entries. Move the flush from __blkg_release() (RCU callback) to blkg_release() (before call_rcu). This ensures the RCU grace period waits for any concurrent flush's rcu_read_lock() section to complete before freeing.
References
Impacted products
Vendor Product Version
Linux Linux Version: 20cb1c2fb7568a6054c55defe044311397e01ddb
Version: 20cb1c2fb7568a6054c55defe044311397e01ddb
Version: 20cb1c2fb7568a6054c55defe044311397e01ddb
Version: 20cb1c2fb7568a6054c55defe044311397e01ddb
Version: 20cb1c2fb7568a6054c55defe044311397e01ddb
Version: 0f6090d90f627d8c58f939067d6c6821ce1b3c68
Version: 6.3.9   ≤
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "block/blk-cgroup.c"
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              "status": "unaffected",
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              "version": "6.18.38",
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              "version": "7.1.3",
              "versionType": "semver"
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
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      "cpeApplicability": [
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          "nodes": [
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              "cpeMatch": [
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                  "vulnerable": true
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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\nblk-cgroup: fix UAF in __blkcg_rstat_flush()\n\nWhen multiple blkgs in the same blkcg are released concurrently,\na use-after-free can occur. The race happens when one blkg\u0027s\n__blkcg_rstat_flush() removes another blkg\u0027s iostat entries via\nllist_del_all(). The second blkg sees an empty list and proceeds\nto free itself while the first is still iterating over its entries.\n\nMove the flush from __blkg_release() (RCU callback) to blkg_release()\n(before call_rcu). This ensures the RCU grace period waits for any\nconcurrent flush\u0027s rcu_read_lock() section to complete before freeing."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Exploitation requires local cgroup management (rmdir on cgroupfs) and concurrent block I/O to populate per-blkcg rstat lists; the vulnerable code is in the block cgroup teardown path, not in any network protocol handler.\nAC:L - The attacker controls both sides of the race by issuing I/O on multiple block devices to create multiple blkgs with pending stats, then concurrently destroying the cgroup to trigger parallel blkg_release() calls on multiple CPUs.\nPR:L - Triggering cgroup deletion and block I/O requires only delegated cgroup write access or namespace/container root (CAP_SYS_ADMIN in a user namespace), not init-namespace root; this is routinely available in containers, Kubernetes pods, and systemd user cgroup hierarchies.\nUI:N - No victim interaction is required; the attacker programmatically performs I/O and cgroup teardown from their own process or container.\nS:U - The UAF corrupts kernel heap memory within the same kernel security domain; it does not inherently cross a VM, container, or IOMMU boundary without a separate privilege-escalation step.\nC:H - The use-after-free dereferences freed blkg structures and associated iostat data during list iteration, enabling arbitrary kernel memory read primitives typical of slab UAF bugs.\nI:H - UAF on kmalloc-allocated blkg objects allows heap grooming and write through dangling pointers, which can be leveraged for arbitrary kernel memory modification or code execution.\nA:H - Concurrent use-after-free during blkg teardown can cause immediate kernel oops/panic from accessing freed memory, and repeated triggering enables reliable denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:51:07.787Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/96e545410c4f74c89d496c1d5d9ef8d08f14368b"
        },
        {
          "url": "https://git.kernel.org/stable/c/bbebd9425cad3573d1527441753899b926525a0f"
        },
        {
          "url": "https://git.kernel.org/stable/c/5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6"
        },
        {
          "url": "https://git.kernel.org/stable/c/afebe44facc48a61761e885bbb7f0380d4a603ec"
        },
        {
          "url": "https://git.kernel.org/stable/c/0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2"
        }
      ],
      "title": "blk-cgroup: fix UAF in __blkcg_rstat_flush()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63802",
    "datePublished": "2026-07-19T12:02:08.020Z",
    "dateReserved": "2026-07-19T07:54:57.013Z",
    "dateUpdated": "2026-08-17T04:51:07.787Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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