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CVE-2026-74731 (GCVE-0-2026-74731)

Vulnerability from cvelistv5 – Published: 2026-08-22 15:33 – Updated: 2026-08-25 05:42
VLAI
Title
sched_ext: Skip sub-disable teardown for never-linked sub-schedulers
Summary
In the Linux kernel, the following vulnerability has been resolved: sched_ext: Skip sub-disable teardown for never-linked sub-schedulers A sub-scheduler enable can fail before scx_link_sched() links the sched into the hierarchy, e.g. when the parent is already being disabled, and cleanup still runs the full scx_sub_disable(). That is racy against root disable: drain_descendants() is the only ordering between a sub's disable-time task walk and root disable's all-task teardown, and an unlinked sub is invisible to it. Root's teardown can thus run between the never-linked sub's drain and its walk, exiting every task to no scheduler. The walk then trips the membership WARN and re-homes the exited tasks onto the dying hierarchy, a use-after-free. Skip the cgroup ownership reset and the task walk if @sch was never linked, indicated by the empty ->sibling as unlinking only happens later in the same function. The membership WARN remains valid: a linked sub is always waited on by an ancestor's drain.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 337ec00b1d9c676f637651c2cefddb8612b867ee , < 6428093a4a986c38c9089b5eb32b56d914ef437a (git)
Affected: 337ec00b1d9c676f637651c2cefddb8612b867ee , < 8c13364db9c9a43ed286f3a8d0fb9477b1adc43c (git)
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Linux Linux Affected: 7.1
Unaffected: 0 , < 7.1 (semver)
Unaffected: 7.1.9 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/sched/ext/ext.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
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              "versionType": "git"
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              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
            }
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        }
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      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
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                  "versionEndExcluding": "7.1.9",
                  "versionStartIncluding": "7.1",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "7.2",
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                  "vulnerable": true
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Skip sub-disable teardown for never-linked sub-schedulers\n\nA sub-scheduler enable can fail before scx_link_sched() links the sched into\nthe hierarchy, e.g. when the parent is already being disabled, and cleanup\nstill runs the full scx_sub_disable().\n\nThat is racy against root disable: drain_descendants() is the only ordering\nbetween a sub\u0027s disable-time task walk and root disable\u0027s all-task teardown,\nand an unlinked sub is invisible to it. Root\u0027s teardown can thus run between\nthe never-linked sub\u0027s drain and its walk, exiting every task to no\nscheduler.\n\nThe walk then trips the membership WARN and re-homes the exited tasks onto\nthe dying hierarchy, a use-after-free.\n\nSkip the cgroup ownership reset and the task walk if @sch was never linked,\nindicated by the empty -\u003esibling as unlinking only happens later in the same\nfunction. The membership WARN remains valid: a linked sub is always waited\non by an ancestor\u0027s drain."
        }
      ],
      "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 - The bug is reached only via local bpf(2) syscalls (BPF_MAP_CREATE/UPDATE_ELEM, BPF_PROG_LOAD, BPF_LINK_CREATE) that register sched_ext_ops struct_ops and invoke scx_enable()/scx_sub_enable_workfn(); per kernel CNA guidance BPF/sched_ext is Local, not network-reachable.\nAC:L - The attacker controls both sides of the race by concurrently attaching a sub-scheduler and closing the root BPF link to trigger scx_root_disable() while never-linked sub cleanup runs scx_sub_disable(); repeated attempts can reliably hit the window between drain_descendants() and the task walk.\nPR:L - Exploitation requires CAP_BPF to create BPF_MAP_TYPE_STRUCT_OPS, load BPF_PROG_TYPE_STRUCT_OPS, and BPF_LINK_CREATE sched_ext; per kernel guidance this is Low because CAP_BPF is obtainable via user namespaces/BPF tokens, not init-namespace root only.\nUI:N - No victim interaction is required; the attacker loads root and sub BPF schedulers, targets their cgroup, and closes BPF links from their own processes to orchestrate the concurrent enable-failure and teardown race.\nS:U - The use-after-free corrupts kernel scheduler/task state during sched_ext teardown on the same host kernel; this is standard kernel memory corruption and privilege escalation impact, not a VM escape or cross-security-authority boundary.\nC:H - Failed never-linked sub cleanup re-homes tasks onto a dying scx_sched hierarchy after root disable frees scheduler state; this use-after-free on scheduler/task metadata can be leveraged for arbitrary kernel memory disclosure per kernel UAF guidance.\nI:H - The UAF during scx_set_task_sched()/scx_enable_task() on a freed scx_sched corrupts scheduler pointers and task ownership in the system-wide scheduler path, enabling heap corruption and arbitrary kernel write or code execution primitives.\nA:H - The race re-homes tasks onto a tearing-down sched_ext hierarchy, tripping membership WARNs and corrupting scheduler teardown; this causes kernel oops/panic/hang on a system-wide scheduler subsystem, which is High availability impact per kernel guidance."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-25T05:42:10.750Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/6428093a4a986c38c9089b5eb32b56d914ef437a"
        },
        {
          "url": "https://git.kernel.org/stable/c/8c13364db9c9a43ed286f3a8d0fb9477b1adc43c"
        }
      ],
      "title": "sched_ext: Skip sub-disable teardown for never-linked sub-schedulers",
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      }
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74731",
    "datePublished": "2026-08-22T15:33:20.294Z",
    "dateReserved": "2026-08-15T05:44:03.930Z",
    "dateUpdated": "2026-08-25T05:42:10.750Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-09-17",
      "epss": "0.00123",
      "percentile": "0.02397"
    },
    "nvd": {
      "cve": {
        "affected": [
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "kernel/sched/ext/ext.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                "versions": [
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                  },
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                  }
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            ],
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          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Skip sub-disable teardown for never-linked sub-schedulers\n\nA sub-scheduler enable can fail before scx_link_sched() links the sched into\nthe hierarchy, e.g. when the parent is already being disabled, and cleanup\nstill runs the full scx_sub_disable().\n\nThat is racy against root disable: drain_descendants() is the only ordering\nbetween a sub\u0027s disable-time task walk and root disable\u0027s all-task teardown,\nand an unlinked sub is invisible to it. Root\u0027s teardown can thus run between\nthe never-linked sub\u0027s drain and its walk, exiting every task to no\nscheduler.\n\nThe walk then trips the membership WARN and re-homes the exited tasks onto\nthe dying hierarchy, a use-after-free.\n\nSkip the cgroup ownership reset and the task walk if @sch was never linked,\nindicated by the empty -\u003esibling as unlinking only happens later in the same\nfunction. The membership WARN remains valid: a linked sub is always waited\non by an ancestor\u0027s drain."
          }
        ],
        "id": "CVE-2026-74731",
        "lastModified": "2026-08-25T06:18:59.753",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-08-22T16:16:48.257",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/6428093a4a986c38c9089b5eb32b56d914ef437a"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/8c13364db9c9a43ed286f3a8d0fb9477b1adc43c"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-25T08:56:38+00:00",
      "cve": "CVE-2026-74731",
      "id": "CVE-2026-74731",
      "initial_release_date": "2026-08-22T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: sched_ext: Skip sub-disable teardown for never-linked sub-schedulers",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74731.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "not set",
      "current_release_date": "2026-08-23T00:03:46Z",
      "cve": "CVE-2026-74731",
      "id": "CVE-2026-74731",
      "initial_release_date": "2026-08-23T00:03:46Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74731",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74731.json",
      "version": "2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.