Vulnerability-Lookup

FKIE_CVE-2021-47505

Vulnerability from fkie_nvd - Published: 2024-05-24 15:15 - Updated: 2026-08-04 10:17

Severity

7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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: aio: fix use-after-free due to missing POLLFREE handling signalfd_poll() and binder_poll() are special in that they use a waitqueue whose lifetime is the current task, rather than the struct file as is normally the case. This is okay for blocking polls, since a blocking poll occurs within one task; however, non-blocking polls require another solution. This solution is for the queue to be cleared before it is freed, by sending a POLLFREE notification to all waiters. Unfortunately, only eventpoll handles POLLFREE. A second type of non-blocking poll, aio poll, was added in kernel v4.18, and it doesn't handle POLLFREE. This allows a use-after-free to occur if a signalfd or binder fd is polled with aio poll, and the waitqueue gets freed. Fix this by making aio poll handle POLLFREE. A patch by Ramji Jiyani <ramjiyani@google.com> (https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com) tried to do this by making aio_poll_wake() always complete the request inline if POLLFREE is seen. However, that solution had two bugs. First, it introduced a deadlock, as it unconditionally locked the aio context while holding the waitqueue lock, which inverts the normal locking order. Second, it didn't consider that POLLFREE notifications are missed while the request has been temporarily de-queued. The second problem was solved by my previous patch. This patch then properly fixes the use-after-free by handling POLLFREE in a deadlock-free way. It does this by taking advantage of the fact that freeing of the waitqueue is RCU-delayed, similar to what eventpoll does.

References

URL	Tags
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72	Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24	Patch
af854a3a-2127-422b-91ae-364da2661108	https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f	Patch
af854a3a-2127-422b-91ae-364da2661108	https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f	Patch
af854a3a-2127-422b-91ae-364da2661108	https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689	Patch
af854a3a-2127-422b-91ae-364da2661108	https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72	Patch
af854a3a-2127-422b-91ae-364da2661108	https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24	Patch

Impacted products

Vendor	Product	Version
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	*
linux	linux_kernel	5.16
linux	linux_kernel	5.16
linux	linux_kernel	5.16
linux	linux_kernel	5.16

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/aio.c",
            "include/uapi/asm-generic/poll.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "321fba81ec034f88aea4898993c1bf15605c023f",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "47ffefd88abfffe8a040bcc1dd0554d4ea6f7689",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "60d311f9e6381d779d7d53371f87285698ecee24",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "50252e4b5e989ce64555c7aef7516bdefc2fea72",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/aio.c",
            "include/uapi/asm-generic/poll.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.18"
            },
            {
              "lessThan": "4.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.19.*",
              "status": "unaffected",
              "version": "4.19.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.4.*",
              "status": "unaffected",
              "version": "5.4.165",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.85",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "5.16",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "2063CE6C-8929-4035-8896-B8ED72601F98",
              "versionEndExcluding": "4.19.221",
              "versionStartIncluding": "4.18",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "B1DD3148-41FC-42AC-96A5-F63D774A97A3",
              "versionEndExcluding": "5.4.165",
              "versionStartIncluding": "4.20",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "D9668578-08F7-4694-A86F-FCE448387A79",
              "versionEndExcluding": "5.10.85",
              "versionStartIncluding": "5.5",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "6664ACE2-F748-4AE5-B98B-58803B0B2C3E",
              "versionEndExcluding": "5.15.8",
              "versionStartIncluding": "5.11",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:5.16:rc1:*:*:*:*:*:*",
              "matchCriteriaId": "357AA433-37E8-4323-BFB2-3038D6E4B414",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:5.16:rc2:*:*:*:*:*:*",
              "matchCriteriaId": "A73429BA-C2D9-4D0C-A75F-06A1CA8B3983",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:5.16:rc3:*:*:*:*:*:*",
              "matchCriteriaId": "F621B5E3-E99D-49E7-90B9-EC3B77C95383",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:5.16:rc4:*:*:*:*:*:*",
              "matchCriteriaId": "F7BFDCAA-1650-49AA-8462-407DD593F94F",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\naio: fix use-after-free due to missing POLLFREE handling\n\nsignalfd_poll() and binder_poll() are special in that they use a\nwaitqueue whose lifetime is the current task, rather than the struct\nfile as is normally the case.  This is okay for blocking polls, since a\nblocking poll occurs within one task; however, non-blocking polls\nrequire another solution.  This solution is for the queue to be cleared\nbefore it is freed, by sending a POLLFREE notification to all waiters.\n\nUnfortunately, only eventpoll handles POLLFREE.  A second type of\nnon-blocking poll, aio poll, was added in kernel v4.18, and it doesn\u0027t\nhandle POLLFREE.  This allows a use-after-free to occur if a signalfd or\nbinder fd is polled with aio poll, and the waitqueue gets freed.\n\nFix this by making aio poll handle POLLFREE.\n\nA patch by Ramji Jiyani \u003cramjiyani@google.com\u003e\n(https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com)\ntried to do this by making aio_poll_wake() always complete the request\ninline if POLLFREE is seen.  However, that solution had two bugs.\nFirst, it introduced a deadlock, as it unconditionally locked the aio\ncontext while holding the waitqueue lock, which inverts the normal\nlocking order.  Second, it didn\u0027t consider that POLLFREE notifications\nare missed while the request has been temporarily de-queued.\n\nThe second problem was solved by my previous patch.  This patch then\nproperly fixes the use-after-free by handling POLLFREE in a\ndeadlock-free way.  It does this by taking advantage of the fact that\nfreeing of the waitqueue is RCU-delayed, similar to what eventpoll does."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: aio: corrige el use-after-free debido a la falta de manejo de POLLFREE. signalfd_poll() y binder_poll() son especiales porque usan una cola de espera cuya duraci\u00f3n es la tarea actual, en lugar de la struct archivo como es normalmente el caso. Esto est\u00e1 bien para bloquear encuestas, ya que una encuesta de bloqueo ocurre dentro de una tarea; sin embargo, las encuestas sin bloqueo requieren otra soluci\u00f3n. Esta soluci\u00f3n consiste en despejar la cola antes de liberarla, enviando una notificaci\u00f3n POLLFREE a todos los camareros. Desafortunadamente, s\u00f3lo eventpoll maneja POLLFREE. Un segundo tipo de encuesta sin bloqueo, aio poll, se agreg\u00f3 en el kernel v4.18 y no maneja POLLFREE. Esto permite que se produzca un use-after-free si se sondea un signalfd o un binder fd con aio poll y se libera la cola de espera. Solucione este problema haciendo que la encuesta de aio se maneje POLLFREE. Un parche de Ramji Jiyani  (https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com) intent\u00f3 hacer esto haciendo que aio_poll_wake() siempre completara la solicitud en l\u00ednea si Se ve POLLFREE. Sin embargo, esa soluci\u00f3n ten\u00eda dos errores. Primero, introdujo un punto muerto, ya que bloque\u00f3 incondicionalmente el contexto aio mientras manten\u00eda el bloqueo de la cola de espera, lo que invierte el orden de bloqueo normal. En segundo lugar, no consider\u00f3 que las notificaciones de POLLFREE se pierdan mientras la solicitud ha sido retirada temporalmente de la cola. El segundo problema lo resolvi\u00f3 mi parche anterior. Luego, este parche corrige adecuadamente el use-after-free al manejar POLLFREE sin interbloqueos. Lo hace aprovechando el hecho de que la liberaci\u00f3n de la cola de espera tiene un retraso de RCU, similar a lo que hace eventpoll."
    }
  ],
  "id": "CVE-2021-47505",
  "lastModified": "2026-08-04T10:17:06.420",
  "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"
      },
      {
        "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": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2021-47505",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2024-06-14T18:37:27.922309Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2024-05-24T15:15:11.000",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72"
    },
    {
      "source": "af854a3a-2127-422b-91ae-364da2661108",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}

CVE-2021-47505 (GCVE-0-2021-47505)

Vulnerability from cvelistv5 – Published: 2024-05-24 15:01 – Updated: 2026-08-05 08:48

Title

aio: fix use-after-free due to missing POLLFREE handling

Summary

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2024-06-14 18:37 UTC

Assigner

Linux mitre root

References

5 references

URL	Tags
https://git.kernel.org/stable/c/321fba81ec034f88a…
https://git.kernel.org/stable/c/4105e6a128e8a9845…
https://git.kernel.org/stable/c/47ffefd88abfffe8a…
https://git.kernel.org/stable/c/60d311f9e6381d779…
https://git.kernel.org/stable/c/50252e4b5e989ce64…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 2c14fa838cbefc23cf1c73ca167ed85b274b2913 , < 321fba81ec034f88aea4898993c1bf15605c023f (git) Affected: 2c14fa838cbefc23cf1c73ca167ed85b274b2913 , < 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f (git) Affected: 2c14fa838cbefc23cf1c73ca167ed85b274b2913 , < 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689 (git) Affected: 2c14fa838cbefc23cf1c73ca167ed85b274b2913 , < 60d311f9e6381d779d7d53371f87285698ecee24 (git) Affected: 2c14fa838cbefc23cf1c73ca167ed85b274b2913 , < 50252e4b5e989ce64555c7aef7516bdefc2fea72 (git)
Linux	Linux	Affected: 4.18 Unaffected: 0 , < 4.18 (semver) Unaffected: 4.19.221 , ≤ 4.19.* (semver) Unaffected: 5.4.165 , ≤ 5.4.* (semver) Unaffected: 5.10.85 , ≤ 5.10.* (semver) Unaffected: 5.15.8 , ≤ 5.15.* (semver) Unaffected: 5.16 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2021-47505",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2024-06-14T18:37:27.922309Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2024-07-30T15:15:43.456Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      },
      {
        "providerMetadata": {
          "dateUpdated": "2024-08-04T05:39:59.807Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/aio.c",
            "include/uapi/asm-generic/poll.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "321fba81ec034f88aea4898993c1bf15605c023f",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "47ffefd88abfffe8a040bcc1dd0554d4ea6f7689",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "60d311f9e6381d779d7d53371f87285698ecee24",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            },
            {
              "lessThan": "50252e4b5e989ce64555c7aef7516bdefc2fea72",
              "status": "affected",
              "version": "2c14fa838cbefc23cf1c73ca167ed85b274b2913",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/aio.c",
            "include/uapi/asm-generic/poll.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.18"
            },
            {
              "lessThan": "4.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.19.*",
              "status": "unaffected",
              "version": "4.19.221",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.4.*",
              "status": "unaffected",
              "version": "5.4.165",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.85",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "5.16",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.19.221",
                  "versionStartIncluding": "4.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.4.165",
                  "versionStartIncluding": "4.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.85",
                  "versionStartIncluding": "4.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.8",
                  "versionStartIncluding": "4.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.16",
                  "versionStartIncluding": "4.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\naio: fix use-after-free due to missing POLLFREE handling\n\nsignalfd_poll() and binder_poll() are special in that they use a\nwaitqueue whose lifetime is the current task, rather than the struct\nfile as is normally the case.  This is okay for blocking polls, since a\nblocking poll occurs within one task; however, non-blocking polls\nrequire another solution.  This solution is for the queue to be cleared\nbefore it is freed, by sending a POLLFREE notification to all waiters.\n\nUnfortunately, only eventpoll handles POLLFREE.  A second type of\nnon-blocking poll, aio poll, was added in kernel v4.18, and it doesn\u0027t\nhandle POLLFREE.  This allows a use-after-free to occur if a signalfd or\nbinder fd is polled with aio poll, and the waitqueue gets freed.\n\nFix this by making aio poll handle POLLFREE.\n\nA patch by Ramji Jiyani \u003cramjiyani@google.com\u003e\n(https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com)\ntried to do this by making aio_poll_wake() always complete the request\ninline if POLLFREE is seen.  However, that solution had two bugs.\nFirst, it introduced a deadlock, as it unconditionally locked the aio\ncontext while holding the waitqueue lock, which inverts the normal\nlocking order.  Second, it didn\u0027t consider that POLLFREE notifications\nare missed while the request has been temporarily de-queued.\n\nThe second problem was solved by my previous patch.  This patch then\nproperly fixes the use-after-free by handling POLLFREE in a\ndeadlock-free way.  It does this by taking advantage of the fact that\nfreeing of the waitqueue is RCU-delayed, similar to what eventpoll does."
        }
      ],
      "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 - Triggered via local syscalls (io_setup/io_submit with IOCB_CMD_POLL on a signalfd or binder fd); not reachable from the network stack or remote protocols.\nAC:L - The attacker fully controls both sides\u2014submitting the aio poll and freeing the waitqueue (e.g. BINDER_THREAD_EXIT, or exiting a task whose sighand owns the queue while the aio context survives via CLONE_VM)\u2014so the UAF is reliably inducible.\nPR:L - io_setup, io_submit, signalfd, and binder ioctls are available to unprivileged users; no CAP_* or root is required along the path.\nUI:N - Exploitation needs no victim action; the attacker performs all setup and teardown themselves.\nS:U - Impact is confined to the local kernel/host authority (standard kernel memory corruption / privilege escalation); it does not cross a VM, IOMMU, or other security boundary.\nC:H - Use-after-free on the waitqueue object enables reclaim and controlled contents, which can be leveraged for arbitrary kernel memory disclosure.\nI:H - The same UAF is exploitable for heap spray and arbitrary write / control-flow hijacking in the kernel, enabling integrity compromise and code execution.\nA:H - Accessing the freed waitqueue lock or structure causes kernel oops/panic even without a full exploit, so availability impact is high."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T08:48:09.163Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f"
        },
        {
          "url": "https://git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f"
        },
        {
          "url": "https://git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689"
        },
        {
          "url": "https://git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24"
        },
        {
          "url": "https://git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72"
        }
      ],
      "title": "aio: fix use-after-free due to missing POLLFREE handling",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2021-47505",
    "datePublished": "2024-05-24T15:01:52.088Z",
    "dateReserved": "2024-05-22T06:20:56.205Z",
    "dateUpdated": "2026-08-05T08:48:09.163Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

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.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

FKIE_CVE-2021-47505

CVE-2021-47505 (GCVE-0-2021-47505)

Tags

Sightings

Nomenclature