CVE-2026-31586 (GCVE-0-2026-31586)

Vulnerability from cvelistv5 – Published: 2026-04-24 14:42 – Updated: 2026-08-05 12:23
VLAI
Title
mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last reference, the blkcg can be freed asynchronously (css_free_rwork_fn -> blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the pointer to access blkcg->online_pin, resulting in a use-after-free: BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531 Workqueue: cgwb_release cgwb_release_workfn Call Trace: <TASK> blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) cgwb_release_workfn (mm/backing-dev.c:629) process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385) Freed by task 1016: kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561) css_free_rwork_fn (kernel/cgroup/cgroup.c:5542) process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385) ** Stack based on commit 66672af7a095 ("Add linux-next specific files for 20260410") I am seeing this crash sporadically in Meta fleet across multiple kernel versions. A full reproducer is available at: https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh (The race window is narrow. To make it easily reproducible, inject a msleep(100) between css_put() and blkcg_unpin_online() in cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the reproducer triggers the splat reliably in less than a second.) Fix this by moving blkcg_unpin_online() before css_put(), so the cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online() accesses it.
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: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 23acef4156c260e8598397a1a2e8b3a23e919893 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 1bd36e93b542d9dd020190c6607c6a3663405195 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 740ba1ebb223f137ff088ab74d533a13f9167bd8 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 115a5266749dcde7fe4127e8623d19c752088f69 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < dfc8292a1d6782c76b626315605e0585a5a18447 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < ea3af09eb87d8f8708c66747fcf1a2762902e839 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 50879a3c1faf06e661090015d59e2127255cff27 (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 67cb119d32f35e32acd0393bbeb318b2bb1fdafe (git)
Affected: 59b57717fff8b562825d9d25e0180ad7e8048ca9 , < 8f5857be99f1ed1fa80991c72449541f634626ee (git)
guessed Create a notification for this product.
Linux Linux Affected: 4.19
Unaffected: 0 , < 4.19 (semver)
Unaffected: 5.10.258 , ≤ 5.10.* (semver)
Unaffected: 5.15.209 , ≤ 5.15.* (semver)
Unaffected: 6.1.175 , ≤ 6.1.* (semver)
Unaffected: 6.6.136 , ≤ 6.6.* (semver)
Unaffected: 6.12.83 , ≤ 6.12.* (semver)
Unaffected: 6.18.24 , ≤ 6.18.* (semver)
Unaffected: 6.19.14 , ≤ 6.19.* (semver)
Unaffected: 7.0.1 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: blk-cgroup: fix use-after-free in cgwb_release_workfn()\n\ncgwb_release_workfn() calls css_put(wb-\u003eblkcg_css) and then later accesses\nwb-\u003eblkcg_css again via blkcg_unpin_online().  If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn -\u003e\nblkcg_css_free -\u003e kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg-\u003eonline_pin, resulting in a use-after-free:\n\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n  Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531\n   Workqueue: cgwb_release cgwb_release_workfn\n   Call Trace:\n    \u003cTASK\u003e\n     blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n     cgwb_release_workfn (mm/backing-dev.c:629)\n     process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)\n\n   Freed by task 1016:\n    kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)\n    css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)\n    process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)\n\n** Stack based on commit 66672af7a095 (\"Add linux-next specific files\nfor 20260410\")\n\nI am seeing this crash sporadically in Meta fleet across multiple kernel\nversions.  A full reproducer is available at:\nhttps://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh\n\n(The race window is narrow.  To make it easily reproducible, inject a\nmsleep(100) between css_put() and blkcg_unpin_online() in\ncgwb_release_workfn().  With that delay and a KASAN-enabled kernel, the\nreproducer triggers the splat reliably in less than a second.)\n\nFix this by moving blkcg_unpin_online() before css_put(), so the\ncgwb\u0027s CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it."
        }
      ],
      "metrics": [
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          "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 vulnerable path is reached by local cgroup/writeback activity: creating/removing cgroup v2 subgroups, moving a task into them, and dirtying files on a block-backed filesystem. There is no network or physical packet/device entry point.\nAC:L - Although the timing window is narrow, the attacker can repeatedly drive both cgroup teardown and cgwb creation/release through cgroup churn and buffered writes. Per the scoring rule for attacker-driven races and UAFs, this is low complexity.\nPR:L - The attacker needs local ability to manipulate a delegated cgroup subtree and run file I/O, which is available to low-privileged users in reasonable delegated cgroup v2 or container/user-slice deployments. It does not require real init-namespace root in those scenarios.\nUI:N - No victim action is required once the attacker has local execution and cgroup access. The attacker triggers creation, writeback, and removal directly.\nS:U - The vulnerability is in the host kernel\u2019s cgroup/writeback lifetime management and impacts the same kernel security authority. Standard local kernel privilege escalation is scored as unchanged scope.\nC:H - The bug is a use-after-free of a freed blkcg object after css_put can lead to blkcg_css_free and kfree before blkcg_unpin_online dereferences it. Kernel UAFs are scored high for confidentiality because reclaimed slab contents can be abused for memory disclosure primitives.\nI:H - The immediate UAF performs a refcount decrement/write through freed memory, and reclaimed-object corruption can plausibly be shaped into broader kernel heap corruption or control-flow compromise. Kernel UAF memory corruption is scored high for integrity.\nA:H - The reported failure is a slab-use-after-free in a kernel worker and can cause an oops, panic, or persistent kernel instability. Repeated local triggering makes availability impact high."
            }
          ]
        }
      ],
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        "dateUpdated": "2026-08-05T12:23:37.101Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893"
        },
        {
          "url": "https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195"
        },
        {
          "url": "https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8"
        },
        {
          "url": "https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69"
        },
        {
          "url": "https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447"
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        {
          "url": "https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839"
        },
        {
          "url": "https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27"
        },
        {
          "url": "https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe"
        },
        {
          "url": "https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee"
        }
      ],
      "title": "mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()",
      "x_generator": {
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31586",
    "datePublished": "2026-04-24T14:42:14.937Z",
    "dateReserved": "2026-03-09T15:48:24.120Z",
    "dateUpdated": "2026-08-05T12:23:37.101Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-31586",
      "date": "2026-10-03",
      "epss": "0.00174",
      "percentile": "0.06203"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-25T02:12:41.000Z",
      "cve": "CVE-2026-31586",
      "id": "msrc_CVE-2026-31586",
      "initial_release_date": "2026-04-26T01:08:52.000Z",
      "product_status:fixed": "1",
      "product_status:known_affected": "4",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-31586.json",
      "version": "7"
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                    "lessThanOrEqual": "7.0.*",
                    "status": "unaffected",
                    "version": "7.0.1",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "*",
                    "status": "unaffected",
                    "version": "7.1",
                    "versionType": "original_commit_for_fix"
                  }
                ]
              }
            ],
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
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                    "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                "negate": false,
                "operator": "OR"
              }
            ]
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        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: blk-cgroup: fix use-after-free in cgwb_release_workfn()\n\ncgwb_release_workfn() calls css_put(wb-\u003eblkcg_css) and then later accesses\nwb-\u003eblkcg_css again via blkcg_unpin_online().  If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn -\u003e\nblkcg_css_free -\u003e kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg-\u003eonline_pin, resulting in a use-after-free:\n\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n  Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531\n   Workqueue: cgwb_release cgwb_release_workfn\n   Call Trace:\n    \u003cTASK\u003e\n     blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n     cgwb_release_workfn (mm/backing-dev.c:629)\n     process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)\n\n   Freed by task 1016:\n    kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)\n    css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)\n    process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)\n\n** Stack based on commit 66672af7a095 (\"Add linux-next specific files\nfor 20260410\")\n\nI am seeing this crash sporadically in Meta fleet across multiple kernel\nversions.  A full reproducer is available at:\nhttps://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh\n\n(The race window is narrow.  To make it easily reproducible, inject a\nmsleep(100) between css_put() and blkcg_unpin_online() in\ncgwb_release_workfn().  With that delay and a KASAN-enabled kernel, the\nreproducer triggers the splat reliably in less than a second.)\n\nFix this by moving blkcg_unpin_online() before css_put(), so the\ncgwb\u0027s CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it."
          }
        ],
        "id": "CVE-2026-31586",
        "lastModified": "2026-06-17T10:34:01.930",
        "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"
              },
              "exploitabilityScore": 1.8,
              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-04-24T15:16:33.393",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
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            "url": "https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
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            "url": "https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Modified",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-416"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-05T13:40:43+00:00",
      "cve": "CVE-2026-31586",
      "id": "CVE-2026-31586",
      "initial_release_date": "2026-04-24T00:00:00+00:00",
      "product_status:known_affected": "260",
      "product_status:under_investigation": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31586.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-11T01:30:27Z",
      "cve": "CVE-2026-31586",
      "id": "CVE-2026-31586",
      "initial_release_date": "2026-04-25T01:38:44Z",
      "product_status:first_fixed": "2",
      "product_status:known_affected": "572",
      "product_status:known_not_affected": "4",
      "product_status:recommended": "648",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-31586",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-31586.json",
      "version": "35"
    }
  }
}



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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.



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.