CVE-2021-47281 (GCVE-0-2021-47281)
Vulnerability from cvelistv5
Published
2024-05-21 14:20
Modified
2026-08-05 08:47
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: ALSA: seq: Fix race of snd_seq_timer_open() The timer instance per queue is exclusive, and snd_seq_timer_open() should have managed the concurrent accesses. It looks as if it's checking the already existing timer instance at the beginning, but it's not right, because there is no protection, hence any later concurrent call of snd_seq_timer_open() may override the timer instance easily. This may result in UAF, as the leftover timer instance can keep running while the queue itself gets closed, as spotted by syzkaller recently. For avoiding the race, add a proper check at the assignment of tmr->timeri again, and return -EBUSY if it's been already registered.
References
Impacted products
Vendor Product Version
Linux Linux Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2021-47281",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2024-05-23T21:20:28.570330Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2024-06-04T17:13:56.494Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      },
      {
        "providerMetadata": {
          "dateUpdated": "2024-08-04T05:32:08.027Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/bd7d88b0874f82f7b29d1a53e574cedaf23166ba"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/536a7646c00a0f14fee49e5e313109e5da2f6031"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/83e197a8414c0ba545e7e3916ce05f836f349273"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "sound/core/seq/seq_timer.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "bd7d88b0874f82f7b29d1a53e574cedaf23166ba",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "536a7646c00a0f14fee49e5e313109e5da2f6031",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "83e197a8414c0ba545e7e3916ce05f836f349273",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "sound/core/seq/seq_timer.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.12"
            },
            {
              "lessThan": "2.6.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.44",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.12.*",
              "status": "unaffected",
              "version": "5.12.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "5.13",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.44",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.12.11",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.13",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: Fix race of snd_seq_timer_open()\n\nThe timer instance per queue is exclusive, and snd_seq_timer_open()\nshould have managed the concurrent accesses.  It looks as if it\u0027s\nchecking the already existing timer instance at the beginning, but\nit\u0027s not right, because there is no protection, hence any later\nconcurrent call of snd_seq_timer_open() may override the timer\ninstance easily.  This may result in UAF, as the leftover timer\ninstance can keep running while the queue itself gets closed, as\nspotted by syzkaller recently.\n\nFor avoiding the race, add a proper check at the assignment of\ntmr-\u003etimeri again, and return -EBUSY if it\u0027s been already registered."
        }
      ],
      "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 through local ioctls on /dev/snd/seq (CREATE_QUEUE, SET_QUEUE_TIMER, SET_QUEUE_CLIENT, close), not via network or adjacent protocols.\nAC:L - The attacker controls both sides of the race by issuing concurrent sequencer ioctls/closes from multiple threads or processes on queues they create, as syzkaller did; success does not depend on victim state outside attacker influence.\nPR:L - Exploitation needs only the ability to open /dev/snd/seq as an unprivileged user (audio group, seat uaccess/ACL, or MIDI-capable app on phones); snd_seq_open imposes no capability checks.\nUI:N - The attacker triggers the race solely with their own open/ioctl/close operations; no action by another user is required.\nS:U - Impact stays within the host kernel authority (local privilege escalation / kernel memory corruption); it does not cross a VM, IOMMU, or other security boundary.\nC:H - The race orphans a running timer whose callback retains a pointer to a freed queue, producing a use-after-free that can be leveraged for arbitrary kernel memory disclosure.\nI:H - The same UAF on the queue object enables heap reuse and control-flow hijacking primitives, so integrity impact is high under kernel memory-corruption guidance.\nA:H - The UAF is observed as a kernel oops in softirq timer context (snd_seq_timer_interrupt), which can crash or hang the system."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T08:47:03.896Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/bd7d88b0874f82f7b29d1a53e574cedaf23166ba"
        },
        {
          "url": "https://git.kernel.org/stable/c/536a7646c00a0f14fee49e5e313109e5da2f6031"
        },
        {
          "url": "https://git.kernel.org/stable/c/83e197a8414c0ba545e7e3916ce05f836f349273"
        }
      ],
      "title": "ALSA: seq: Fix race of snd_seq_timer_open()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2021-47281",
    "datePublished": "2024-05-21T14:20:07.499Z",
    "dateReserved": "2024-05-21T13:27:52.128Z",
    "dateUpdated": "2026-08-05T08:47:03.896Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://git.kernel.org/stable/c/bd7d88b0874f82f7b29d1a53e574cedaf23166ba\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/536a7646c00a0f14fee49e5e313109e5da2f6031\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/83e197a8414c0ba545e7e3916ce05f836f349273\", \"tags\": [\"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T05:32:08.027Z\"}}, {\"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-47281\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2024-05-23T21:20:28.570330Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2024-05-23T21:20:32.592Z\"}, \"title\": \"CISA ADP Vulnrichment\"}], \"cna\": {\"title\": \"ALSA: seq: Fix race of snd_seq_timer_open()\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"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\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"AV:L - The bug is reached through local ioctls on /dev/snd/seq (CREATE_QUEUE, SET_QUEUE_TIMER, SET_QUEUE_CLIENT, close), not via network or adjacent protocols.\\nAC:L - The attacker controls both sides of the race by issuing concurrent sequencer ioctls/closes from multiple threads or processes on queues they create, as syzkaller did; success does not depend on victim state outside attacker influence.\\nPR:L - Exploitation needs only the ability to open /dev/snd/seq as an unprivileged user (audio group, seat uaccess/ACL, or MIDI-capable app on phones); snd_seq_open imposes no capability checks.\\nUI:N - The attacker triggers the race solely with their own open/ioctl/close operations; no action by another user is required.\\nS:U - Impact stays within the host kernel authority (local privilege escalation / kernel memory corruption); it does not cross a VM, IOMMU, or other security boundary.\\nC:H - The race orphans a running timer whose callback retains a pointer to a freed queue, producing a use-after-free that can be leveraged for arbitrary kernel memory disclosure.\\nI:H - The same UAF on the queue object enables heap reuse and control-flow hijacking primitives, so integrity impact is high under kernel memory-corruption guidance.\\nA:H - The UAF is observed as a kernel oops in softirq timer context (snd_seq_timer_interrupt), which can crash or hang the system.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\", \"lessThan\": \"bd7d88b0874f82f7b29d1a53e574cedaf23166ba\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\", \"lessThan\": \"536a7646c00a0f14fee49e5e313109e5da2f6031\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\", \"lessThan\": \"83e197a8414c0ba545e7e3916ce05f836f349273\", \"versionType\": \"git\"}], \"programFiles\": [\"sound/core/seq/seq_timer.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"2.6.12\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"2.6.12\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.44\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.12.11\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.12.*\"}, {\"status\": \"unaffected\", \"version\": \"5.13\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"sound/core/seq/seq_timer.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/bd7d88b0874f82f7b29d1a53e574cedaf23166ba\"}, {\"url\": \"https://git.kernel.org/stable/c/536a7646c00a0f14fee49e5e313109e5da2f6031\"}, {\"url\": \"https://git.kernel.org/stable/c/83e197a8414c0ba545e7e3916ce05f836f349273\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nALSA: seq: Fix race of snd_seq_timer_open()\\n\\nThe timer instance per queue is exclusive, and snd_seq_timer_open()\\nshould have managed the concurrent accesses.  It looks as if it\u0027s\\nchecking the already existing timer instance at the beginning, but\\nit\u0027s not right, because there is no protection, hence any later\\nconcurrent call of snd_seq_timer_open() may override the timer\\ninstance easily.  This may result in UAF, as the leftover timer\\ninstance can keep running while the queue itself gets closed, as\\nspotted by syzkaller recently.\\n\\nFor avoiding the race, add a proper check at the assignment of\\ntmr-\u003etimeri again, and return -EBUSY if it\u0027s been already registered.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.44\", \"versionStartIncluding\": \"2.6.12\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.12.11\", \"versionStartIncluding\": \"2.6.12\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.13\", \"versionStartIncluding\": \"2.6.12\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T08:47:03.896Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-47281\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T08:47:03.896Z\", \"dateReserved\": \"2024-05-21T13:27:52.128Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-05-21T14:20:07.499Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.